International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 9.5, pp. 790-811
https://doi.org/10.1107/97809553602060000621

Chapter 9.5. Typical interatomic distances: organic compounds

F. H. Allen,a D. G. Watson,a L. Brammer,b A. G. Orpenc and R. Taylora

aCambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, England,bDepartment of Chemistry, University of Missouri–St Louis, 8001 Natural Bridge Road, St Louis, MO 63121-4499, USA, and cSchool of Chemistry, University of Bristol, Bristol BS8 1TS, England

Mean bond lengths for organic compounds, derived from the Cambridge Structural Database, are tabulated for 625 different bond types involving the elements C, H, N, O, B, F, P, S, Cl, As, Se, Br, Te and I. Associated statistical information characterizes each of the distributions, which are derived from both X-ray and neutron diffraction data.

9.5.1. Introduction

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The determination of molecular geometry is of vital importance to our understanding of chemical structure and bonding. The majority of experimental data have come from X-ray and neutron diffraction, microwave spectroscopy, and electron diffraction. Over the years, compilations of results from these techniques have appeared sporadically. The first major compilation was Chemical Society Special Publication No. 11: Tables of Interatomic Distances and Configuration in Molecules and Ions (Sutton, 1958[link]). This volume summarized results obtained by diffraction and spectroscopic methods prior to 1956; a supplementary volume (Sutton, 1965[link]) extended this coverage to 1959. Summary tables of bond lengths between carbon and other elements were also published in Volume III of International Tables for X-ray Crystallography (Kennard, 1962[link]). Some years later, the Cambridge Crystallographic Data Centre (Allen, Bellard, Brice, Cartwright, Doubleday, Higgs, Hummelink, Hummelink-Peters, Kennard, Motherwell, Rodgers & Watson, 1979[link]) produced an atlas-style compendium of all organic, organometallic and metal-complex crystal structures published in the period 1960–1965 (Kennard, Watson, Allen, Isaacs, Motherwell, Pettersen & Town, 1972[link]). More recently, a survey of geometries determined by spectroscopic methods (Harmony, Laurie, Kuczkowski, Schwendemann, Ramsay, Lovas, Lafferty & Maki, 1979[link]) has extended coverage in this area to mid-1977.

The production of further comprehensive compendia of X-ray and neutron diffraction results has been precluded by the steep rise in the number of published crystal structures, as illustrated by Fig. 9.5.1.1[link]. Printed compilations have been effectively superseded by computerized databases. In particular, the Cambridge Structural Database now (1991) contains bibliographic, chemical, and numerical results for some 86 000 organo-carbon crystal structures. This machine-readable file fulfils the function of a comprehensive structure-by-structure compendium of molecular geometries. However, the amount of data now held in the CSD is so large that there is also a need for concise, printed tabulations of average molecular dimensions.

[Figure 9.5.1.1]

Figure 9.5.1.1 | top | pdf |

Growth of the Cambridge Structural Database 1965–1985 as number of entries (Nent) published in a given year.

The only tables of average geometry in general use are those contained in Sutton (1958[link], 1965[link]) which list mean bond lengths for a variety of atom pairs and functional groups. Since these early tables were based on data obtained before 1960, we have used the CSD to prepare a new table of average bond lengths in organic compounds. Table 9.5.1.1[link] given here specifically lists average lengths for bonds involving the elements H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and I. Mean values are presented for 682 different bond types involving these elements.

Table 9.5.1.1| top | pdf |
Average lengths (Å) for bonds involving the elements H, B, C, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and I

BondSubstructuredmσqlqunNote
As(3)—As(3) X2AsAsX2 2.459 2.457 0.011 2.456 2.466 8  
As—B see CUDLOC (2.065), CUDLUI (2.041)              
As—Br see CODDEE, CODDII (2.346–3.203)              
As(4)—C X3AsCH3 1.903 1.907 0.016 1.893 1.916 12  
(X)2(C, O, S=)AsCsp3 1.927 1.929 0.017 1.921 1.937 16
AsCar in Ph4As+ 1.905 1.909 0.012 1.897 1.912 108
(X)2(C, O, S=)AsCar 1.922 1.927 0.016 1.908 1.934 36
As(3)—C X2AsCsp3 1.963 1.965 0.017 1.948 1.978 6  
X2AsCar 1.956 1.956 0.015 1.944 1.964 41  
As(3)—Cl X2AsCl 2.268 2.256 0.039 2.247 2.281 10  
As(6)—F in [{\bf AsF}^-_6] 1.678 1.676 0.020 1.659 1.695 36  
As(3)—I see OPIMAS (2.579, 2.590)              
As(3)—N(3) X2AsNX2 1.858 1.858 0.029 1.839 1.873 19  
As(4)=N(2) see TPASSN (1.837)              
As(4)—O (X)2(O=)AsOH 1.710 1.712 0.017 1.695 1.726 6  
As(3)—O see ASAZOC, PHASOC01 (1.787–1.845)              
As(4)=O X3As=O 1.661 1.661 0.016 1.652 1.667 9  
As(3)—P(3) see BELNIP (2.350, 2.362)            
As(3)=P(3) see BUTHAZ10 (2.124)            
As(3)—S X2AsS 2.275 2.266 0.032 2.247 2.298 14  
As(4)=S X3As=S 2.083 2.082 0.004 2.080 2.086 9  
As(3)—Se(2) see COSDIX, ESEARS (2.355–2.401)            
As(3)—Si(4) see BICGEZ, MESIAD (2.351–2.365)            
As(3)—Te(2) see ETEARS (2.571, 2.576)            
B(n)—B(n) n = 5–7 in boron cages 1.775 1.773 0.031 1.763 1.786 688  
B(4)—B(4) see CETTAW (2.041)              
B(4)—B(3) see COFVOI (1.698)              
B(3)—B(3) X2BBX2 1.701 1.700 0.014 1.691 1.712 8  
B(6)—Br   1.967 1.971 0.014 1.954 1.979 7
B(4)—Br   2.017 2.008 0.031 1.990 2.044 15
B(n)—C n = 5–7: BC in cages 1.716 1.717 0.020 1.707 1.728 96  
n = 3–4: BCsp3 not cages 1.597 1.599 0.022 1.585 1.611 29 1
n = 4: BCar 1.606 1.607 0.012 1.596 1.615 41  
n = 4: BCar in Ph4B 1.643 1.643 0.006 1.641 1.645 16  
n = 3: BCar 1.556 1.552 0.015 1.546 1.566 24  
B(n)—Cl B(5)—Cl and B(3)—Cl 1.751 1.751 0.011 1.743 1.761 14  
B(4)—Cl 1.833 1.833 0.013 1.821 1.843 22  
B(4)—F BF (B neutral) 1.366 1.368 0.017 1.356 1.375 25  
BF in [{\rm BF}^-_4] 1.365 1.372 0.029 1.352 1.390 84  
B(4)—I see TMPBTI (2.220, 2.253)              
B(4)—N(3) X3BN(=C)(X) 1.611 1.617 0.013 1.601 1.625 8  
in pyrazaboles 1.549 1.552 0.015 1.536 1.560 10  
B(3)—N(3) X2BN—C2: all coplanar 1.404 1.404 0.014 1.389 1.408 40 2
for τ(BN) > 30° see BOGSUL, BUSHAY, CILRUK (1.434–1.530)              
S2BNX2 1.447 1.443 0.013 1.435 1.470 14  
B(4)—O BO in [{\rm BO}^-_4] 1.468 1.468 0.022 1.453 1.479 24  
for neutral BO see Note 3             3
B(3)—O(2) X2BOX 1.367 1.367 0.024 1.349 1.382 35  
B(n)—P n = 4: BP 1.922 1.927 0.027 1.900 1.954 10  
n = 3: see BUPSIB10 (1.892, 1.893)              
B(4)—S B(4)—S(3) 1.930 1.927 0.009 1.925 1.934 10  
B(4)—S(2) 1.896 1.896 0.004 1.893 1.899 6  
B(3)—S N—BS2 1.806 1.806 0.010 1.799 1.816 28  
(=X—)(N—)BS 1.851 1.854 0.013 1.842 1.859 10  
Br—Br see BEPZEB, TPASTB 2.542 2.548 0.015 2.526 2.551 4  
Br—C BrC* 1.966 1.967 0.029 1.951 1.983 100 4
BrCsp3 (cyclopropane) 1.910 1.910 0.010 1.900 1.914 8  
BrCsp2 1.883 1.881 0.015 1.874 1.894 31 4
BrCar (mono-Br + m,p-Br2) 1.899 1.899 0.012 1.892 1.906 119 4
BrCar (o-Br2) 1.875 1.872 0.011 1.864 1.884 8 4
Br(2)—Cl see TEACBR (2.362–2.402)            
Br—I see DTHIBR10 (2.646), TPHOSI (2.695)              
Br—N see NBBZAM (1.843)              
Br—O see CIYFOF 1.581 1.581 0.007 1.574 1.587 4  
Br—P see CISTED (2.366)              
Br—S(2) see BEMLIO (2.206)            
Br—S(3) see CIWYIQ (2.435, 2.453)            
Br—S(3)+ see THINBR (2.321)            
Br—Se see CIFZUM (2.508, 2.619)              
Br—Si see BIZJAV (2.284)              
Br—Te In Br6Te2−see CUGBAH (2.692–2.716)              
BrTe(4) see BETUTE10 (3.079, 3.015)              
BrTe(3) see BTUPTE (2.835)              
Csp3—Csp3 C#CH2CH3 1.513 1.514 0.014 1.507 1.523 192  
(C#)2CH—CH3 1.524 1.526 0.015 1.518 1.534 226  
(C#)3CCH3 1.534 1.534 0.011 1.527 1.541 825  
C#CH2CH2—C# 1.524 1.524 0.014 1.516 1.532 2459  
(C#)2CH—CH2—C# 1.531 1.531 0.012 1.524 1.538 1217  
(C#)3CCH2—C# 1.538 1.539 0.010 1.533 1.544 330  
(C#)2CH—CH—(C#)2 1.542 1.542 0.011 1.536 1.549 321  
(C#)3CCH—(C#)2 1.556 1.556 0.011 1.549 1.562 215  
(C#)3CC—(C#)3 1.588 1.580 0.025 1.566 1.610 21  
C*C* (overall) 1.530 1.530 0.015 1.521 1.539 5777 5, 6
in cyclopropane (any substituent) 1.510 1.509 0.026 1.497 1.523 888 7
in cyclobutane (any substituent) 1.554 1.553 0.021 1.540 1.567 679 8
in cyclopentane (C,H substituents) 1.543 1.543 0.018 1.532 1.554 1641  
in cyclohexane (C,H substituents) 1.535 1.535 0.016 1.525 1.545 2814  
cyclopropyl—C* (exocyclic) 1.518 1.518 0.019 1.505 1.531 366 7
cyclobutyl—C* (exocyclic) 1.529 1.529 0.016 1.519 1.539 376 8
cyclopentyl—C* (exocyclic) 1.540 1.541 0.017 1.527 1.549 956  
cyclohexyl—C* (exocyclic) 1.539 1.538 0.016 1.529 1.549 2682  
in cyclobutene (any substituent) 1.573 1.574 0.017 1.566 1.586 25 8
in cyclopentene (C,H substituents) 1.541 1.539 0.015 1.532 1.549 208  
in cyclohexene (C,H substituents) 1.541 1.541 0.020 1.528 1.554 586  
in oxirane (epoxide) 1.466 1.466 0.015 1.458 1.474 249 9
in aziridine 1.480 1.481 0.021 1.465 1.496 67 9
in oxetane 1.541 1.541 0.019 1.527 1.557 16  
in azetidine 1.548 1.543 0.018 1.536 1.558 22  
oxiranyl—C* (exocyclic) 1.509 1.507 0.018 1.497 1.519 333 9
aziridinyl—C* (exocyclic) 1.512 1.512 0.018 1.496 1.526 13 9
Csp3—Csp2 CH3C=C 1.503 1.504 0.011 1.497 1.509 215  
C#CH2C=C 1.502 1.502 0.013 1.494 1.510 483  
(C#)2CH—C=C 1.510 1.510 0.014 1.501 1.518 564  
(C#)3CC=C 1.522 1.522 0.016 1.511 1.533 193  
C*—C=C (overall) 1.507 1.507 0.015 1.499 1.517 1456 5
C*—C=C (endocylic):              
 in cyclopropene 1.509 1.508 0.016 1.500 1.516 20 10
 in cyclobutene 1.513 1.512 0.018 1.500 1.525 50 8
 in cyclopentene 1.512 1.512 0.014 1.502 1.521 208  
 in cyclohexene 1.506 1.505 0.016 1.495 1.516 391  
 in cyclopentadiene 1.502 1.503 0.019 1.490 1.515 18  
 in cyclohexa-1,3-diene 1.504 1.504 0.017 1.491 1.517 56  
C*C[triple bond]C (exocyclic):              
 cyclopropenyl—C* 1.478 1.475 0.012 1.470 1.485 7 10
 cyclobutenyl—C* 1.489 1.483 0.015 1.479 1.496 11 8
 cyclopentenyl—C* 1.504 1.506 0.012 1.495 1.512 115  
 cyclohexenyl—C* 1.511 1.511 0.013 1.502 1.519 292  
C*CH=O in aldehydes 1.510 1.510 0.008 1.501 1.518 7  
(C*)2C=O in ketones 1.511 1.511 0.015 1.501 1.521 952 11
(C*)2C=O in cyclobutanone 1.529 1.530 0.016 1.514 1.545 18  
(C*)2C=O in cyclopentanone 1.514 1.514 0.016 1.505 1.523 312  
(C*)2C=O acyclic and 6+ rings 1.509 1.509 0.016 1.499 1.519 626  
C*—COOH in carboxylic acids 1.502 1.502 0.014 1.495 1.510 176  
C*—COO in carboxylate anions 1.520 1.521 0.011 1.516 1.528 57  
C*—C(=O)(—OC*) in acyclic esters 1.497 1.496 0.018 1.484 1.509 553 12
C*—C(=O)(—OC*) in β-lactones 1.519 1.519 0.020 1.500 1.538 4 13
C*—C(=O)(—OC*) in γ-lactones 1.512 1.512 0.015 1.501 1.521 110 12
C*—C(=O)(—OC*) in δ-lactones 1.504 1.502 0.013 1.495 1.517 27 12
cyclopropyl (C)—C=O in ketones, acids, and esters 1.486 1.485 0.018 1.474 1.497 105 7
C*C(=O)(—NH2) in acyclic amides 1.514 1.512 0.016 1.506 1.526 32 14
C*C(=O)(—NHC*) in acyclic amides 1.506 1.505 0.012 1.498 1.515 78 14
C*C(=O)[—N(C*)2] in acyclic amides 1.505 1.505 0.011 1.496 1.517 15 14
Csp3—Car CH3Car 1.506 1.507 0.011 1.501 1.513 454  
C#CH2Car 1.510 1.510 0.009 1.505 1.516 674  
(C#)2CCar 1.515 1.515 0.011 1.508 1.522 363  
(C#)3CCar 1.527 1.530 0.016 1.517 1.539 308  
C*Car (overall) 1.513 1.513 0.014 1.505 1.521 1813  
cyclopropyl (C)—Car 1.490 1.490 0.015 1.479 1.503 90 7
Csp3—Csp1 C*—C[triple bond]C 1.466 1.465 0.010 1.460 1.469 21 15
C#C[triple bond]C 1.472 1.472 0.012 1.464 1.481 88 15
C*—C[triple bond]N 1.470 1.469 0.013 1.463 1.479 106 7(b)
cyclopropyl (C)—C[triple bond]N 1.444 1.447 0.010 1.436 1.451 38 7
Csp2—Csp2 C=CC=C (conjugated) 1.455 1.455 0.011 1.447 1.463 30 16, 18
C=CC=C (unconjugated) 1.478 1.476 0.012 1.470 1.479 8 17, 18
C=CC=C (overall) 1.460 1.460 0.015 1.450 1.470 38  
C=CC=CC=C 1.443 1.445 0.013 1.431 1.454 29 18
C=CC=C (endocyclic in TCNQ) 1.432 1.433 0.012 1.424 1.441 280 19
C=CC(=O)(—C*) (conjugated) 1.464 1.462 0.018 1.453 1.476 211 16, 18
C=CC(=O)(—C*) (unconjugated) 1.484 1.486 0.017 1.475 1.497 14 17, 18
C=CC(=O)(—C*) (overall) 1.465 1.462 0.018 1.453 1.478 226  
C=CC(=O)—C=C:              
 in benzoquinone (C,H substituents only) 1.478 1.476 0.011 1.469 1.488 28  
 in benzoquinone (any substituent) 1.478 1.478 0.031 1.464 1.498 172  
 non-quinonoid 1.456 1.455 0.012 1.447 1.464 28  
C—CCOOH 1.475 1.476 0.015 1.461 1.488 22  
C=CCOOC* 1.488 1.489 0.014 1.478 1.497 113  
C=CCOO 1.502 1.499 0.017 1.488 1.510 11  
HOOCCOOH 1.538 1.537 0.007 1.535 1.541 9  
HOOCCOO 1.549 1.552 0.009 1.546 1.553 13  
OOCCOO 1.564 1.559 0.022 1.554 1.568 9  
formal Csp2—Csp2 single bond in selected, non-fused heterocycles:              
 in 1H-pyrrole  (C3—C4) 1.412 1.410 0.016 1.401 1.427 29  
 in furan  (C3—C4) 1.423 1.423 0.016 1.412 1.433 62  
 in thiophene  (C3—C4) 1.424 1.425 0.015 1.415 1.433 40  
 in pyrazole  (C3—C4) 1.410 1.412 0.016 1.400 1.418 20  
 in isoxazole  (C3—C4) 1.425 1.425 0.016 1.413 1.438 9  
 in furazan  (C3—C4) 1.428 1.427 0.007 1.422 1.435 6  
 in furoxan  (C3—C4) 1.417 1.417 0.006 1.412 1.422 14  
Csp2—Car C=CCar  (conjugated) 1.470 1.470 0.015 1.463 1.480 37 16, 18
C=CCar  (unconjugated) 1.488 1.490 0.012 1.480 1.496 87 17, 18
C=CCar  (overall) 1.483 1.483 0.015 1.472 1.494 124  
cyclopropenyl (C=C)—Car 1.447 1.448 0.006 1.441 1.452 8 10
CarC(=O)—C* 1.488 1.489 0.016 1.478 1.500 84  
CarC(=O)—Car 1.480 1.481 0.017 1.468 1.494 58  
CarCOOH 1.484 1.485 0.014 1.474 1.491 75  
CarC(=O)(—OC*) 1.487 1.487 0.012 1.480 1.494 218  
CarCOO 1.504 1.509 0.014 1.495 1.512 26  
CarC(=O)—NH2 1.500 1.503 0.020 1.498 1.510 19  
CarC=N—C#  (conjugated) 1.476 1.478 0.014 1.466 1.486 27 16
CarC=N—C# (unconjugated) 1.491 1.490 0.008 1.485 1.496 48 17
CarC=N—C# (overall) 1.485 1.487 0.013 1.481 1.493 75  
in indole (C3—C3a) 1.434 1.434 0.011 1.428 1.439 40  
Csp2—Csp1 C=CC[triple bond]C 1.431 1.427 0.014 1.425 1.441 11 7(b)
C=CC[triple bond]N in TCNQ 1.427 1.427 0.010 1.420 1.433 280 19
Car—Car in biphenyls (ortho substituent all H) 1.487 1.488 0.007 1.484 1.493 30  
 ([\ge 1] non-H ortho substituent) 1.490 1.491 0.010 1.486 1.495 212  
Car—Csp1 CarC[triple bond]C 1.434 1.436 0.006 1.430 1.437 37  
CarC[triple bond]N 1.443 1.444 0.008 1.436 1.448 31  
Csp1—Csp1 C[triple bond]CC[triple bond]C 1.377 1.378 0.012 1.374 1.384 21  
Csp2=Csp2 C*—CH=CH2 1.299 1.300 0.027 1.280 1.311 42  
(C*)2C=CH2 1.321 1.321 0.013 1.313 1.328 77  
C*—CH=CH—C* (cis) 1.317 1.318 0.013 1.310 1.323 106  
C*—CH=CH—C* (trans) 1.312 1.311 0.011 1.304 1.320 19  
C*—CH=CH—C* (overall) 1.316 1.317 0.015 1.309 1.323 127  
(C*)2C=CH—C* 1.326 1.328 0.011 1.319 1.334 168  
(C*)2C=C—(C*)2 1.331 1.330 0.009 1.326 1.334 89  
(C*,H)2C=C—(C*,H)2 (overall) 1.322 1.323 0.014 1.315 1.331 493 5
in cyclopropene (any substituent) 1.294 1.288 0.017 1.284 1.302 10 10
in cyclobutene (any substituent) 1.335 1.335 0.019 1.324 1.347 25 8
in cyclopentene (C,H substituents) 1.323 1.324 0.013 1.314 1.331 104  
in cyclohexene (C,H substituents) 1.326 1.325 0.012 1.318 1.334 196  
C=C=C (allenes, any substituents) 1.307 1.307 0.005 1.303 1.310 18  
C=CC=C (C,H substituents, conjugated) 1.330 1.330 0.014 1.322 1.338 76 16
C=CC=CC=C (C,H substituents, conjugated) 1.345 1.345 0.012 1.337 1.350 58 16
C=C—Car (C,H substituents, conjugated) 1.339 1.340 0.011 1.334 1.346 124 16
C=C in cyclopenta-1,3-diene (any substituent) 1.341 1.341 0.017 1.328 1.356 18  
C=C in cyclohexa-1,3-diene (any substituent) 1.332 1.332 0.013 1.323 1.341 56  
in C=C—C=O (C,H substituent, conjugated) 1.340 1.340 0.013 1.332 1.348 211 16, 18
in C=C—C=O (C,H substituent, unconjugated) 1.331 1.330 0.008 1.326 1.339 14 17, 18
in C=C—C=O (C,H substituent, overall) 1.340 1.339 0.013 1.332 1.348 226  
in cyclohexa-2,5-dien-1-ones 1.329 1.327 0.011 1.321 1.335 28  
in p-benzoquinones (C*,H substituents) 1.333 1.337 0.011 1.325 1.338 14  
in p-benzoquinones (any substituent) 1.349 1.339 0.030 1.330 1.364 86  
in TCNQ (endocyclic) 1.352 1.353 0.010 1.345 1.358 142 19
in TCNQ (exocyclic) 1.392 1.391 0.017 1.379 1.405 139 19
C=C—OH in enol tautomers 1.362 1.360 0.020 1.349 1.370 54  
in heterocycles (any substituent)              
 1H-pyrrole (C2—C3, C4—C5) 1.375 1.377 0.018 1.361 1.388 58  
 furan  (C2—C3, C4—C5) 1.341 1.342 0.021 1.329 1.351 125  
 thiophene  (C2—C3, C4—C5) 1.362 1.359 0.025 1.346 1.377 60  
 pyrazole  (C4—C5) 1.369 1.372 0.019 1.362 1.383 20  
 imidazole  (C4—C5) 1.360 1.361 0.014 1.352 1.367 44  
 isoxazole  (C4—C5) 1.341 1.336 0.012 1.331 1.355 9  
 indole  (C2—C3) 1.364 1.363 0.012 1.355 1.371 40  
Car[\ddb]Car in phenyl rings with C*,H substituents only:              
 H—C[\ddb]C—H 1.380 1.381 0.013 1.372 1.388 2191  
 C*—C[\ddb]C—H 1.387 1.388 0.010 1.382 1.393 891  
 C*—C[\ddb]C—C* 1.397 1.397 0.009 1.392 1.403 182  
 C[\ddb]C (overall) 1.384 1.384 0.013 1.375 1.391 3264  
F—C[\ddb]C—F 1.372 1.374 0.011 1.366 1.380 84 4
Cl—C[\ddb]C—Cl 1.388 1.389 0.014 1.380 1.398 152 4
in naphthalene (D2h) C1—C2 1.364 1.364 0.014 1.356 1.373 440  
 (any substituent) C2—C3 1.406 1.406 0.014 1.397 1.415 218  
 (any substituent) C1—C8a 1.420 1.419 0.012 1.412 1.426 440  
 (any substituent) C4a—C8a 1.422 1.424 0.011 1.417 1.429 109  
in anthracene (D2h) C1—C2 1.356 1.356 0.009 1.350 1.360 56  
 (any substituent) C2—C3 1.410 1.410 0.010 1.401 1.416 34  
 (any substituent) C1—C9a 1.430 1.430 0.006 1.426 1.434 56  
 (any substituent) C4a—C9a 1.435 1.436 0.007 1.429 1.440 34  
 (any substituent) C9—C9a 1.400 1.402 0.009 1.395 1.406 68  
in pyridine (C,H substituent) 1.379 1.381 0.012 1.371 1.387 276 20
in pyridine (any substituents) 1.380 1.380 0.015 1.371 1.389 537 20
in pyridinium cation:              
 (N+—H; C,H substituents on C) C2—C3 1.373 1.375 0.012 1.368 1.380 30  
 (N+—H; C,H substituents on C) C3—C4 1.379 1.380 0.011 1.371 1.388 30  
 (N+X; C,H substituents on C) C2—C3 1.373 1.372 0.019 1.362 1.382 151  
 (N+X; C,H substituents on C) C3—C4 1.383 1.385 0.019 1.372 1.394 151  
in pyrazine (H substituent on C) 1.379 1.377 0.010 1.370 1.388 10  
in pyrazine (any substituent on C) 1.405 1.405 0.024 1.388 1.420 60  
in pyrimidine (C,H substituents on C) 1.387 1.389 0.018 1.379 1.400 28  
Csp1[triple bond]Csp1 XC[triple bond]CX 1.183 1.183 0.014 1.174 1.193 119 15
C,H—C[triple bond]C—C,H 1.181 1.181 0.014 1.173 1.192 104 15
in C[triple bond]C—C(sp2, ar) 1.189 1.193 0.010 1.181 1.195 38 15
in C[triple bond]CC[triple bond]C 1.192 1.192 0.010 1.187 1.197 42 15
in CH[triple bond]C—C# 1.174 1.174 0.011 1.167 1.180 42 15
Csp3—Cl Omitting 1,2-dichlorides:              
 C—CH2Cl 1.790 1.790 0.007 1.783 1.795 13 4
 C2CH—Cl 1.803 1.802 0.003 1.800 1.807 8 4
 C3CCl 1.849 1.856 0.011 1.837 1.858 5 4
 XCH2Cl (X = C,H,N,O) 1.790 1.791 0.011 1.783 1.797 37 4
 X2CH—Cl (X = C,H,N,O) 1.805 1.803 0.014 1.800 1.812 26 4
 X3CCl (X = C,H,N,O) 1.843 1.838 0.014 1.835 1.858 7 4
 X2CCl2 (X = C,H,N,O) 1.779 1.776 0.015 1.769 1.790 18 4
 XCCl3 (X = C,H,N,O) 1.768 1.765 0.011 1.761 1.776 33 4
 ClCH(—C)—CH(—C)—Cl 1.793 1.793 0.013 1.786 1.800 66 4
 ClC(—C2)—C(—C2)—Cl 1.762 1.760 0.010 1.757 1.765 54 4
 cyclopropyl—Cl 1.755 1.756 0.011 1.749 1.763 64  
Csp2—Cl C=CCl (C,H,N,O substituents on C) 1.734 1.729 0.019 1.719 1.748 63 4
C=CCl2 (C,H,N,O substituents on C) 1.720 1.716 0.013 1.708 1.729 20 4
ClC=CCl 1.713 1.711 0.011 1.705 1.720 80 4
Car—Cl CarCl (mono-Cl + m,p-Cl2) 1.739 1.741 0.010 1.734 1.745 340 4
CarCl (o-Cl2) 1.720 1.720 0.010 1.713 1.717 364 4
Csp1—Cl see HCLENE10 (1.634, 1.646)              
Csp3—F Omitting 1,2-difluorides:              
 C—CH2F and C2CH—F 1.399 1.399 0.017 1.389 1.408 25 4
 C3CF 1.428 1.431 0.009 1.421 1.435 11 4
 (C*,H)2CF2 1.349 1.347 0.012 1.342 1.356 58 4
 C*—CF3 1.336 1.334 0.007 1.330 1.344 12 4
 FC*—C*—F 1.371 1.374 0.007 1.362 1.375 26 4
 X3CF (X = C,H,N,O) 1.386 1.389 0.033 1.373 1.408 70 4
 X2CF2 (X = C,H,N,O) 1.351 1.349 0.013 1.342 1.356 58 4
 XCF3 (X = C,H,N,O) 1.322 1.323 0.015 1.314 1.332 309 4
 FC(—X)2C(—X)2F (X = C,H,N,O) 1.373 1.374 0.009 1.362 1.377 30 4
 FC(—X)2—NO2 (X = any substituent) 1.320 1.319 0.009 1.312 1.327 18  
Csp2—F C=CF (C,H,N,O substituents on C) 1.340 1.340 0.013 1.334 1.346 34 4
Car—F CarF (mono-F + m,p-F2) 1.363 1.362 0.008 1.357 1.368 38 4
CarF (o-F2) 1.340 1.340 0.009 1.336 1.344 167 4
Csp3—H C—CH3 (methyl) 1.059 1.061 0.030 1.039 1.083 83 21
C2CH2 (primary) 1.092 1.095 0.013 1.088 1.099 100 21
C3CH (secondary) 1.099 1.097 0.004 1.095 1.103 14 21
C2,3CH (primary and secondary) 1.093 1.095 0.012 1.089 1.100 118 21
XCH3 (methyl) 1.066 1.074 0.028 1.049 1.087 160 21
X2CH2 (primary) 1.092 1.095 0.012 1.088 1.099 230 21
X3CH (secondary) 1.099 1.099 0.007 1.095 1.103 117 21
X2,3CH (primary and secondary) 1.094 1.096 0.011 1.091 1.100 348 21
Csp2—H C—C=CH 1.077 1.079 0.012 1.074 1.085 14 21
Car—H CarH 1.083 1.083 0.011 1.080 1.087 218 21
Csp3—I C*I 2.162 2.159 0.015 2.149 2.179 15 4
Car—I CarI 2.095 2.095 0.015 2.089 2.104 51 4
Csp3—N(4) C*NH[^+_3] 1.488 1.488 0.013 1.482 1.495 298  
(C*)2NH[^+_2] 1.494 1.493 0.016 1.484 1.503 249  
(C*)3NH+ 1.502 1.502 0.015 1.491 1.512 509  
(C*)4N+ 1.510 1.509 0.020 1.496 1.523 319  
C*N+ (overall) 1.499 1.498 0.018 1.488 1.510 1370  
Csp3—N(3) C*N+ in N-substituted pyridinium 1.485 1.484 0.009 1.477 1.490 32  
C*NH2 (Nsp3: pyramidal) 1.469 1.470 0.010 1.462 1.474 19 22
(C*)2NH (Nsp3: pyramidal) 1.469 1.467 0.012 1.461 1.477 152 5, 22
(C*)3N (Nsp3: pyramidal) 1.469 1.468 0.014 1.460 1.476 1042 5, 22
C*Nsp3 (overall) 1.469 1.468 0.014 1.460 1.476 1201  
Csp3Nsp3 in aziridine 1.472 1.471 0.016 1.464 1.482 134  
Csp3Nsp3 in azetidine 1.484 1.481 0.018 1.472 1.495 21  
Csp3Nsp3 in tetrahydropyrrole 1.475 1.473 0.016 1.464 1.483 66  
Csp3Nsp3 in piperidine 1.473 1.473 0.013 1.460 1.479 240  
Csp3—Nsp2 (N planar) in:             23
 acyclic amides C*NH—C=O 1.454 1.451 0.011 1.446 1.461 78 14
 β-lactams C*N(—X)—C=O (endo) 1.464 1.465 0.012 1.458 1.475 23 13
 γ-lactams C*NH—C=O (endo) 1.457 1.458 0.011 1.449 1.465 20 13
 γ-lactams C*N(—C*)—C=O (endo) 1.462 1.461 0.010 1.453 1.466 15 13
 γ-lactams C*N(—C*)—C=O (exo) 1.458 1.456 0.014 1.448 1.465 15 13
 δ-lactams C*NH—C=O (endo) 1.478 1.472 0.016 1.467 1.491 6 14
 δ-lactams C*N(—C*)—C=O (endo) 1.479 1.476 0.007 1.475 1.482 15 14
 δ-lactams C*N(—C*)—C=O (exo) 1.468 1.471 0.009 1.462 1.477 15 14
 nitro compounds (1,2-dinitro omitted):              
 C—CH2NO2 1.485 1.483 0.020 1.478 1.502 8  
 C2CH—NO2 1.509 1.509 0.011 1.502 1.511 12  
 C3CNO2 1.533 1.533 0.013 1.530 1.539 17  
 C2C—(NO2)2 1.537 1.536 0.016 1.525 1.550 19  
 1,2-dinitro: NO2C*C*NO2 1.552 1.550 0.023 1.536 1.572 32  
Csp3—N(2) C#N=N 1.493 1.493 0.020 1.477 1.506 54  
C*N=C—Car 1.465 1.468 0.011 1.461 1.472 75  
Csp2—N(3) C=CNH2 Nsp2 planar 1.336 1.344 0.017 1.317 1.348 10 23
C=CNH—C# Nsp2 planar 1.339 1.340 0.016 1.327 1.351 17 23
C=CN—(C#)2 Nsp2 planar 1.355 1.358 0.014 1.341 1.363 22 23
C=CN—(C#)2 Nsp3 pyramidal 1.416 1.418 0.018 1.397 1.432 18 22
Csp2—Nsp2 (N planar) in:             23
 acyclic amides NH2C=O 1.325 1.323 0.009 1.318 1.331 32 14
 acyclic amides C*—NH—C=O 1.334 1.333 0.011 1.326 1.343 78 14
 acyclic amides (C*)2NC=O 1.346 1.342 0.011 1.339 1.356 5 14
 β-lactams C*—NH—C=O 1.385 1.388 0.019 1.374 1.396 23 13
 γ-lactams C*—NH—C=O 1.331 1.331 0.011 1.326 1.337 20 13
 γ-lactams C*—N(—C*)—C=O 1.347 1.344 0.014 1.335 1.359 15 13
 δ-lactams C*—NH—C=O 1.334 1.334 0.006 1.330 1.339 6 14
 δ-lactams C*—N(—C*)—C=O 1.352 1.353 0.010 1.344 1.356 15 14
 peptides C#N(—X)—C(—C#)(=O) 1.333 1.334 0.013 1.326 1.340 380 24
 ureas (NH2)2C=O 1.334 1.334 0.008 1.329 1.339 48 25, 26
 ureas (C#NH)2C=O 1.347 1.345 0.010 1.341 1.354 26 25
 ureas [(C#)nN]2C=O 1.363 1.359 0.014 1.354 1.370 40 25, 27
 thioureas (X2N)2C=S 1.346 1.343 0.023 1.328 1.361 192  
 imides [C#C(=O)]2NH 1.376 1.377 0.012 1.369 1.383 64  
 imides [C#C(=O)]2N—C# 1.389 1.383 0.017 1.376 1.404 38  
 imides [Csp2C(=O)]2N—C# 1.396 1.396 0.010 1.389 1.403 46  
 imides [Csp2C(=O)]2N—Csp2 1.409 1.406 0.020 1.391 1.419 28  
 guanidinium [C—(NH2)3]+ (unsubstituted) 1.321 1.320 0.008 1.314 1.327 39  
 guanidinium [C—(NH2)3]+ (any substituent) 1.328 1.325 0.015 1.317 1.333 140  
 in heterocyclic systems (any substituent):              
  1H-pyrrole (N1—C2, N1—C5) 1.372 1.374 0.016 1.363 1.384 58  
  indole (N1—C2) 1.370 1.370 0.012 1.364 1.377 40  
  pyrazole (N1—C5) 1.357 1.359 0.012 1.347 1.365 20  
  imidazole (N1—C2) 1.349 1.349 0.018 1.338 1.358 44  
  imidazole (N1—C5) 1.370 1.370 0.010 1.365 1.377 44  
Csp2—N(2) in imidazole (N3—C4) 1.376 1.377 0.011 1.369 1.384 44  
Car—N(4) CarN+(C,H)3 1.465 1.466 0.007 1.461 1.470 23  
Car—N(3) CarNH2 (Nsp2: planar) 1.355 1.360 0.020 1.340 1.372 33 23
CarNH2 (Nsp3: pyramidal) 1.394 1.396 0.011 1.385 1.403 25 22
CarNH2 (overall) 1.375 1.377 0.025 1.363 1.394 98 28
CarNH—C# (Nsp2: planar) 1.353 1.353 0.007 1.347 1.359 16 23
CarNH—C# (Nsp3: pyramidal) 1.419 1.423 0.017 1.412 1.432 8 22
CarNH—C# (overall) 1.380 1.364 0.032 1.353 1.412 31 28
CarN—(C#)2 (Nsp2: planar) 1.371 1.370 0.016 1.363 1.382 41 23
CarN—(C#)2 (Nsp3: pyramidal) 1.426 1.425 0.011 1.421 1.431 22 22
CarN—(C#)2 (overall) 1.390 1.385 0.030 1.366 1.420 69 28
in indole (N1—C7a) 1.372 1.372 0.007 1.367 1.376 40  
CarNO2 1.468 1.469 0.014 1.460 1.476 556  
Car—N(2) CarN=N 1.431 1.435 0.020 1.422 1.442 26  
Csp2=N(3) in furoxan (+N2=C3) 1.316 1.316 0.009 1.311 1.324 14  
Csp2=N(2) CarC=N—C# 1.279 1.279 0.008 1.275 1.285 75  
(C,H)2C=N—OH in oximes 1.281 1.280 0.013 1.273 1.288 67  
S—C=NX 1.302 1.302 0.021 1.285 1.319 36  
in pyrazole (N2=C3) 1.329 1.331 0.014 1.315 1.339 20  
in imidazole (C2=N3) 1.313 1.314 0.011 1.307 1.319 44  
in isoxazole (N2=C3) 1.314 1.315 0.009 1.305 1.320 9  
in furazan (N2=C3, C4=N5) 1.298 1.299 0.006 1.294 1.303 12  
in furoxan (C4=N5) 1.304 1.306 0.008 1.300 1.308 14  
Car[\ddb]N(3) C[\ddb]N+—H (pyrimidinium) 1.335 1.334 0.015 1.325 1.342 30  
C[\ddb]N+—C* (pyrimidinium) 1.346 1.346 0.010 1.340 1.352 64  
C[\ddb]N+—O (pyrimidinium) 1.362 1.359 0.013 1.353 1.369 56  
Car[\ddb]N(2) C[\ddb]N (pyridine) 1.337 1.338 0.012 1.300 1.344 269  
C[\ddb]N (pyrazine) 1.336 1.335 0.022 1.319 1.347 120  
C[\ddb]N[\ddb]C (pyrimidine) 1.339 1.338 0.015 1.333 1.342 28  
N[\ddb]C[\ddb]N (pyrimidine) 1.333 1.335 0.013 1.326 1.337 28  
C[\ddb]N (pyrimidine) (overall) 1.336 1.337 0.014 1.331 1.339 56  
in any six-membered N-containing  aromatic ring:              
 H—C[\ddb]N[\ddb]C—H 1.334 1.334 0.014 1.327 1.341 146  
 H—C[\ddb]N[\ddb]C—C* 1.339 1.341 0.013 1.336 1.345 38  
 C*—C[\ddb]N[\ddb]C—C* 1.345 1.345 0.008 1.342 1.348 24  
 C[\ddb]N[\ddb]C (overall) 1.336 1.337 0.014 1.329 1.344 204  
Csp1[triple bond]N(2) XN+[triple bond]C (isocyanide) 1.144 1.147 0.006 1.140 1.148 6  
Csp1[triple bond]N(1) C*—C[triple bond]N 1.136 1.137 0.010 1.131 1.142 140  
C=C—C[triple bond]N in TCNQ 1.144 1.144 0.008 1.139 1.149 284 19
CarC[triple bond]N 1.138 1.138 0.007 1.133 1.143 31  
X—S—C[triple bond]N 1.144 1.141 0.012 1.138 1.151 10  
(S—C[triple bond]N) 1.155 1.156 0.012 1.147 1.165 14  
Csp3—O(2) in alcohols:              
 CH3OH 1.413 1.414 0.018 1.395 1.425 17  
 C—CH2OH 1.426 1.426 0.011 1.420 1.431 75  
 C2CH—OH 1.432 1.431 0.011 1.425 1.439 266  
 C3COH 1.440 1.440 0.012 1.432 1.449 106  
 C*OH (overall) 1.432 1.431 0.013 1.424 1.441 464  
in dialkyl ethers:             29
 CH3O—C* 1.416 1.418 0.016 1.405 1.426 110  
 C—CH2O—C* 1.426 1.424 0.011 1.418 1.435 34  
 C2CH—O—C* 1.429 1.430 0.010 1.420 1.437 53  
 C3CO—C* 1.452 1.450 0.011 1.445 1.458 39  
 C*—OC* (overall) 1.426 1.425 0.019 1.414 1.437 236 5
in aryl alkyl ethers:             29
 CH3O—Car 1.424 1.424 0.012 1.417 1.431 616  
 C—CH2O—Car 1.431 1.430 0.013 1.422 1.438 188  
 C2CH—O—Car 1.447 1.446 0.020 1.435 1.466 58  
 C3CO—Car 1.470 1.469 0.018 1.456 1.483 55  
 C*O—Car (overall) 1.429 1.427 0.018 1.419 1.436 917  
in alkyl esters of carboxylic acids:             12, 29
 CH3O—C(=O)—C* 1.448 1.449 0.010 1.442 1.455 200  
 C—CH2O—C(=O)—C* 1.452 1.453 0.009 1.445 1.458 32  
 C2CH—O—C(=O)—C* 1.460 1.460 0.010 1.454 1.465 78  
 C3CO—C(=O)—C* 1.477 1.475 0.008 1.472 1.484 6  
 C*O—C(=O)—C* (overall) 1.450 1.451 0.014 1.442 1.459 314  
in alkyl esters of α,β-unsaturated acids:              
 C*O—C(=O)—C=C (overall) 1.453 1.452 0.013 1.444 1.459 112  
in alkyl esters of benzoic acid:              
 C*O—C(=O)—C(phenyl) (overall) 1.454 1.454 0.012 1.446 1.463 219  
in ring systems:              
 oxirane (epoxide) (any substituent) 1.446 1.446 0.014 1.438 1.456 498 9
 oxetane (any substituent) 1.463 1.460 0.015 1.451 1.474 16  
 tetrahydrofuran (C,H substituents) 1.442 1.441 0.017 1.430 1.451 154  
 tetrahydropyran (C,H substituents) 1.441 1.442 0.015 1.431 1.451 22  
 β-lactones: C*—O—C(=O) 1.492 1.494 0.010 1.481 1.501 4 16
 γ-lactones: C*—O—C(=O) 1.464 1.464 0.012 1.455 1.473 110 12
 δ-lactones: C*—O—C(=O) 1.461 1.464 0.017 1.452 1.473 27 12
O—C—O systems in gem-diols, and pyranose and furanose sugars:             30, 31
 HOC*OH 1.397 1.401 0.012 1.388 1.405 18  
C5O5C1O1H in pyranoses:              
 O1 axial (α): C5—O5 1.439 1.440 0.008 1.432 1.445 29  
 O1 axial (α): O5—C1 1.427 1.426 0.012 1.421 1.432 29  
 O1 axial (α): C1—O1 1.403 1.400 0.012 1.391 1.412 29  
 O1 equatorial (β): C5—O5 1.435 1.436 0.008 1.429 1.440 17  
 O1 equatorial (β): O5—C1 1.430 1.431 0.010 1.424 1.436 17  
 O1 equatorial (β): C1—O1 1.393 1.393 0.007 1.386 1.399 17  
 α + β (overall): C5—O5 1.439 1.440 0.008 1.432 1.446 60  
 α + β (overall): O5—C1 1.430 1.429 0.012 1.421 1.436 60  
 α + β (overall): C1—O1 1.401 1.399 0.011 1.392 1.407 60  
C4O4C1O1H in furanoses:              
 (overall values) C4—O4 1.442 1.446 0.012 1.436 1.449 18  
 (overall values) O4—C1 1.432 1.432 0.012 1.421 1.443 18  
 (overall values) C1—O1 1.404 1.405 0.013 1.397 1.409 18  
C5O5C1O1—C* in pyranoses:              
 O1 axial (α): C5—O5 1.439 1.438 0.010 1.433 1.446 67  
 O1 axial (α): O5—C1 1.417 1.417 0.009 1.410 1.424 67  
 O1 axial (α): C1—O1 1.409 1.409 0.014 1.401 1.417 67  
 O1 axial (α): O1—C* 1.435 1.435 0.013 1.427 1.443 67  
 O1 equatorial (β): C5—O5 1.434 1.435 0.006 1.429 1.439 39  
 O1 equatorial (β): O5—C1 1.424 1.424 0.008 1.418 1.431 39  
 O1 equatorial (β): C1—O1 1.390 1.390 0.011 1.381 1.400 39  
 O1 equatorial (β): O1—C* 1.437 1.438 0.013 1.428 1.445 39  
 α + β (overall): C5—O5 1.436 1.436 0.009 1.431 1.442 126  
 α + β (overall): O5—C1 1.419 1.419 0.011 1.412 1.426 126  
 α + β (overall): C1—O1 1.402 1.403 0.016 1.391 1.413 126  
 α + β (overall): O1—C* 1.436 1.436 0.013 1.428 1.445 126  
C4O4C1O1C* in furanoses:              
 (overall values) C4—O4 1.443 1.445 0.013 1.429 1.453 23  
 (overall values) O4—C1 1.421 1.418 0.012 1.413 1.431 23  
 (overall values) C1—O1 1.410 1.409 0.014 1.401 1.420 23  
 (overall values) O1—C* 1.439 1.437 0.014 1.429 1.449 23  
Miscellaneous:              
 C#O—SiX3 1.416 1.416 0.017 1.405 1.428 29  
 C*O—SO2—C 1.465 1.461 0.014 1.454 1.475 33  
Csp2—O(2) in enols:  C=COH 1.333 1.331 0.017 1.324 1.342 53  
in enol esters:  C=CO—C* 1.354 1.353 0.016 1.341 1.363 40  
in acids:  C*—C(=O)—OH 1.308 1.311 0.019 1.298 1.320 174  
in acids:  C=C—C(=O)—OH 1.293 1.295 0.019 1.279 1.307 22  
in acids:  CarC(=O)—OH 1.305 1.311 0.020 1.291 1.317 75  
in esters:  C*—C(=O)—O—C* 1.336 1.337 0.014 1.328 1.346 551 12, 29
in esters:  C=C—C(=O)—O—C* 1.332 1.331 0.011 1.324 1.339 112  
in esters:  CarC(=O)—O—C* 1.337 1.335 0.013 1.329 1.344 219 12
in esters:  C*—C(=O)—O—C=C 1.362 1.359 0.018 1.351 1.374 26  
in esters:  C*—C(=O)—O—C=C 1.407 1.405 0.017 1.394 1.420 26  
in esters:  C*—C(=O)—O—Car 1.360 1.359 0.011 1.355 1.367 40 12
in anhydrides: O=COC=O 1.386 1.386 0.011 1.379 1.393 70  
in ring systems:              
 furan  (O1—C2, O1—C5) 1.368 1.369 0.015 1.359 1.377 125  
 isoxazole (O1—C5) 1.354 1.354 0.010 1.345 1.360 9  
 β-lactones: C*—C(=O)—O—C* 1.359 1.359 0.013 1.348 1.371 4 13
 γ-lactones: C*—C(=O)—O—C* 1.350 1.349 0.012 1.342 1.359 110 12
 δ-lactones: C*—C(=O)—O—C* 1.339 1.339 0.016 1.332 1.347 27 12
Car—O(2) in phenols: CarOH 1.362 1.364 0.015 1.353 1.373 511  
in aryl alkyl ethers: CarO—C* 1.370 1.370 0.011 1.363 1.377 920 29, 32
in diaryl ethers: CarOCar 1.384 1.381 0.014 1.375 1.391 132  
in esters: CarO—C(=O)—C* 1.401 1.401 0.010 1.394 1.408 40 12
Csp2=O(1) in aldehydes and ketones:              
 C*—CH=O 1.192 1.912 0.005 1.188 1.197 7  
 (C*)2C=O 1.210 1.210 0.008 1.206 1.215 474 5
 (C#)2C=O in cyclobutanones 1.198 1.198 0.007 1.194 1.204 12  
 (C#)2C=O in cyclopentanones 1.208 1.208 0.007 1.203 1.212 155  
 (C#)2C=O in cyclohexanones 1.211 1.211 0.009 1.207 1.216 312  
 C=C—C=O 1.222 1.222 0.010 1.216 1.229 225  
 (C=C)2C=O 1.233 1.229 0.010 1.226 1.242 28  
 CarC=O 1.221 1.218 0.014 1.212 1.229 85  
 (Car)2C=O 1.230 1.226 0.015 1.220 1.238 66  
 C=O in benzoquinones 1.222 1.220 0.013 1.211 1.231 86  
delocalized double bonds in carboxylate anions:              
 H—C[\ddb]O[^-_2] (formate) 1.242 1.243 0.012 1.234 1.252 24  
 C*—C[\ddb]O[^-_2] 1.254 1.253 0.010 1.247 1.261 114  
 C=C—C[\ddb]O[^-_2] 1.250 1.248 0.017 1.238 1.261 52  
 CarC[\ddb]O[^-_2] 1.255 1.253 0.010 1.249 1.262 22  
 HOOC—C[\ddb]O[^-_2] (hydrogen oxalate) 1.243 1.247 0.015 1.232 1.256 26  
 O2[\ddb]CC[\ddb]O[^-_2] (oxalate) 1.251 1.251 0.007 1.248 1.254 18  
in carboxylic acids (X—COOH):              
 C*—C(=O)—OH 1.214 1.214 0.019 1.203 1.224 175  
 C=C—C(=O)—OH 1.229 1.226 0.017 1.218 1.237 22  
 CarC(=O)—OH 1.226 1.223 0.020 1.211 1.241 75  
in esters:              
 C*—C(=O)—O—C* 1.196 1.196 0.010 1.190 1.202 551 12
 C=C—C(=O)—O—C* 1.199 1.198 0.009 1.193 1.203 113  
 CarC(=O)—O—C* 1.202 1.201 0.009 1.196 1.207 218 12
 C*—C(=O)—O—C=C 1.190 1.190 0.014 1.184 1.198 26  
 C*—C(=O)—O—Car 1.187 1.188 0.011 1.181 1.195 40 12
in anhydrides: O=C—O—C=O 1.187 1.187 0.010 1.184 1.193 70  
in β-lactones: C*—C(=O)—O—C* 1.193 1.193 0.006 1.187 1.198 4 13
 γ-lactones: C*—C(=O)—O—C* 1.201 1.202 0.009 1.196 1.206 109 12
 δ-lactones: C*—C(=O)—O—C* 1.205 1.207 0.008 1.201 1.209 27 12
in amides:              
 NH2C(—C*)=O 1.234 1.233 0.012 1.225 1.243 32 14
 (C*—)(C*,H—)N—C(—C*)=O 1.231 1.231 0.012 1.224 1.238 378 14
 β-lactams: C*—NH—C=O 1.198 1.200 0.012 1.193 1.204 23 13
 γ-lactams: C*—NH—C=O 1.235 1.235 0.008 1.232 1.240 20 13
 γ-lactams: C*—N(—C*)—C=O 1.225 1.226 0.011 1.217 1.233 15 13
 δ-lactams: C*—NH—C=O 1.240 1.241 0.003 1.237 1.243 6 14
 δ-lactams: O*—N(—C*)—C=O 1.233 1.233 0.007 1.229 1.239 15 14
in ureas:              
 (NH2)2C=O 1.256 1.256 0.007 1.249 1.261 24 25, 26
 (C#—NH)2C=O 1.241 1.237 0.011 1.235 1.245 13 25
 [(C#)n—N]2C=O 1.230 1.230 0.007 1.224 1.234 20 25, 27
Csp3—P(4) C3P+C* 1.800 1.802 0.015 1.790 1.812 35 33
C2P(=O)—CH3 1.791 1.790 0.006 1.786 1.795 10  
C2P(=O)—CH2—C 1.806 1.806 0.009 1.801 1.813 45  
C2P(=O)—CH—C2 1.821 1.821 0.009 1.815 1.828 15  
C2P(=O)—C—C3 1.841 1.842 0.008 1.835 1.847 14  
C2P(=O)—C* (overall) 1.813 1.811 0.017 1.800 1.822 84  
Csp3—P(3) C2PC* 1.855 1.857 0.019 1.840 1.870 23  
Car—P(4) C3P+Car 1.793 1.792 0.011 1.786 1.800 276  
C2P(=O)—Car 1.801 1.802 0.011 1.796 1.807 98  
Ph3P=N+=PPh3 1.795 1.795 0.008 1.789 1.800 197  
Car—P(3) C2PCar 1.836 1.837 0.010 1.830 1.844 102  
(N[\ddb])2PCar (P[\ddb]N aromatic) 1.795 1.793 0.011 1.788 1.803 43  
Csp3—S(4) C*SO2—C (C* = CH3 excluded) 1.786 1.782 0.018 1.774 1.797 75  
C*SO2—C (overall) 1.779 1.778 0.020 1.764 1.790 94  
C*—SO2—O—X 1.745 1.744 0.009 1.738 1.754 7 34
C*SO2—N—X2 1.758 1.736 0.018 1.746 1.773 17 34
Csp3—S(3) C*S(=O)—C (C* = CH3 excluded) 1.818 1.814 0.024 1.802 1.829 69  
C*S(=O)—C (overall) 1.809 1.806 0.025 1.793 1.820 88  
CH3S+[X_{2}] 1.786 1.787 0.007 1.779 1.792 21  
C*S+X2 (C* = CH3 excluded) 1.823 1.820 0.016 1.812 1.834 18  
C*S+—C2 (overall) 1.804 1.794 0.025 1.788 1.820 41  
Csp3—S(2) C*—SH 1.808 1.805 0.010 1.800 1.819 6  
CH3S—C* 1.789 1.787 0.008 1.784 1.794 9  
C—CH2S—C* 1.817 1.816 0.013 1.808 1.824 92  
C2CH—S—C* 1.819 1.819 0.011 1.811 1.825 32  
C3CS—C* 1.856 1.860 0.011 1.854 1.863 26  
C*SC* (overall) 1.819 1.817 0.019 1.809 1.827 242  
in thiirane 1.834 1.835 0.025 1.810 1.858 4 9
in thietane: see ZCMXSP (1.817, 1.844)              
in tetrahydrothiophene 1.827 1.826 0.018 1.811 1.837 20  
in tetrahydrothiopyran 1.823 1.821 0.014 1.812 1.832 24  
C—CH2S—S—X 1.823 1.820 0.014 1.813 1.832 41  
C3CS—S—X 1.863 1.865 0.015 1.848 1.878 11  
C*S—S—X (overall) 1.833 1.828 0.022 1.818 1.848 59  
Csp2—S(2) C=CS—C* 1.751 1.755 0.017 1.740 1.764 61  
C=CS—C=C (in tetrathiafulvalene) 1.741 1.741 0.011 1.733 1.750 88  
C=CS—C=C (in thiophene) 1.712 1.712 0.013 1.703 1.722 60  
O=CS—C# 1.762 1.759 0.018 1.747 1.778 20  
Car—S(4) CarSO2—C 1.763 1.764 0.009 1.756 1.769 96  
CarSO2—O—X 1.752 1.750 0.008 1.749 1.756 27  
CarSO2—N—X2 1.758 1.759 0.013 1.749 1.765 106 35
Car—S(3) CarS(=O)—C 1.790 1.790 0.010 1.783 1.798 41  
CarS+X2 1.778 1.779 0.010 1.771 1.787 10  
Car—S(2) CarS—C* 1.773 1.774 0.009 1.765 1.779 44  
CarSCar 1.768 1.767 0.010 1.762 1.774 158  
CarSCar (in phenothiazine) 1.764 1.764 0.008 1.760 1.769 48  
CarS—S—X 1.777 1.777 0.012 1.767 1.785 47  
Csp1—S(2) N[triple bond]CSX 1.679 1.683 0.026 1.645 1.698 10  
Csp1—S(1) (N[triple bond]CS) 1.630 1.630 0.014 1.619 1.641 14  
Csp2=S(1) (C*)2C=S: see IPMUDS (1.599)              
(Car)2C=S: see CELDOM (1.611)              
(X)2C=S (X = C,N,O,S) 1.671 1.675 0.024 1.656 1.689 245  
X2N—C(=S)—S—X 1.660 1.660 0.016 1.648 1.674 38  
(X2N)2C=S (thioureas) 1.681 1.684 0.020 1.669 1.693 96  
N—C([\ddb]S)2 1.720 1.721 0.012 1.709 1.731 20  
Csp3—Se C#Se 1.970 1.967 0.032 1.948 1.998 21  
Csp2—Se(2) C=CSeC=C (in tetraselenafulvalene) 1.893 1.895 0.013 1.882 1.902 32  
Car—Se(3) Ph3Se+ 1.930 1.929 0.006 1.924 1.936 13  
Csp3—Si(5) C#SiX4 1.874 1.876 0.015 1.859 1.884 9  
Csp3—Si(4) CH3SiX3 1.857 1.857 0.018 1.848 1.869 552  
C*SiX3 (C* = CH3 excluded) 1.888 1.887 0.023 1.872 1.905 124  
C*SiX2 (overall) 1.863 1.861 0.024 1.850 1.875 681  
Car—Si(4) CarSiX3 1.868 1.868 0.014 1.857 1.878 178  
Csp1—Si(4) C[triple bond]CSiX3 1.837 1.840 0.012 1.824 1.849 8  
Csp3—Te C#Te 2.158 2.159 0.030 2.128 2.177 13  
Car—Te CarTe 2.116 2.115 0.020 2.104 2.130 72  
Csp2=Te see CEDCUJ (2.044)              
Cl—Cl see PHASCL (2.306, 2.227)              
Cl—I see CMBIDZ (2.563), HXPASC (2.541, 2.513), METAMM (2.552), BQUINI (2.416, 2.718)              
Cl—N see BECTAE (1.743–1.757), BOGPOC (1.705)              
Cl—O(1) in ClO[^-_4] 1.414 1.419 0.026 1.403 1.431 252  
Cl—P (N[\ddb])2PCl (N[\ddb]P aromatic) 1.997 1.994 0.015 1.989 2.004 46  
ClP (overall) 2.008 2.001 0.035 1.986 2.028 111  
Cl—S ClS (overall) 2.072 1.079 0.023 2.047 2.091 6  
see also longer bonds in CILSAR (2.283), BIHXIZ (2.357), CANLUY (2.749)              
Cl—Se See BIRGUE10, BIRHAL10, CTCNSE (2.234–2.851)              
Cl—Si(4) ClSiX3 (monochloro) 2.072 2.075 0.009 2.066 2.078 5  
Cl2SiX2 and Cl3SiX 2.020 2.012 0.015 2.007 2.036 5  
Cl—Te Cl—Te in range 2.34–2.60 2.520 2.515 0.034 2.493 2.537 22 36
see also longer bonds in BARRIV, BOJPUL, CETUTE, EPHTEA, OPNTEC10 (2.73–2.94)              
F—N(3) FN—C2 and F2N—C 1.406 1.404 0.016 1.395 1.416 9  
F—P(6) in hexafluorophosphate, PF[^-_6] 1.579 1.587 0.025 1.563 1.598 72  
P—P(3) (N[\ddb])2PF (N[\ddb]P aromatic) 1.495 1.497 0.016 1.481 1.510 10  
F—S 43 observations in range 1.409–1.770 in a wide variety of environments              
FS(6) in F2SO2—C2 (see FPSULF10, BETJOZ) 1.640 1.646 0.011 1.626 1.649 6  
FS(4) in F2S(=O)—N (see BUDTEZ) 1.527 1.528 0.004 1.524 1.530 24 37
F—Si(6) in SiF[^{2-}_6] 1.694 1.701 0.013 1.677 1.703 6  
F—Si(5) FSiX4 1.636 1.639 0.035 1.602 1.657 10  
F—Si(4) FSiX3 1.588 1.587 0.014 1.581 1.599 24  
F—Te see CUCPIZ [F—Te(6) = 1.942, 1.937], FPHTEL [F—Te(4) = 2.006]              
H—N(4) X3N+H 1.033 1.036 0.022 1.026 1.045 87 21
H—N(3) X2NH 1.009 1.010 0.019 0.997 1.023 95 21
H—O(2) in alcohols C*—OH 0.967 0.969 0.010 0.959 0.974 63 21
in alcohols C#OH 0.967 0.970 0.010 0.959 0.974 73 21
in acids O=C—OH 1.015 1.017 0.017 1.001 1.031 16 21, 38
I—I in [{\rm I}^-_3] 2.917 2.918 0.011 2.907 2.927 6  
I—N see BZPRIB, CMBIDZ, HMTITI, HMTNTI, IFORAM, IODMAM (2.042–2.475)              
I—O XIO (see BZPRIB, CAJMAB, IBZDAC11) for IO[^-_6] see BOVMEE (1.829–1.912) 2.144 2.144 0.028 2.127 2.164 6  
I—P(3) see CEHKAB (2.490–2.493)            
I—S see DTHIBR10 (2.687), ISUREA10 (2.629), BZTPPI (3.251)              
I—Te(4) ITeX3 2.926 2.928 0.026 2.902 2.944 8  
N(4)—N(3) X3N+N0X2 (N0 planar) 1.414 1.414 0.005 1.412 1.418 13  
N(3)—N(3) (C)(C,H)—NaNb—(C)(C,H)             5, 39
Na, Nb pyramidal 1.454 1.452 0.021 1.444 1.457 44 40
Na pyramidal, Nb planar 1.420 1.420 0.015 1.407 1.433 68 40
Na, Nb planar 1.401 1.401 0.018 1.384 1.418 40 40
overall 1.425 1.425 0.027 1.407 1.443 139  
N(3)—N(2) in pyrazole (N1—N2) 1.366 1.366 0.019 1.350 1.375 20  
in pyridazinium (N1+[\ddb]N2) 1.350 1.349 0.010 1.345 1.361 7  
N(2)[\ddb]N(2) N[\ddb]N (aromatic) in pyridazine              
with C,H as ortho substituents 1.304 1.300 0.019 1.287 1.326 6  
with N,Cl as ortho substituents 1.368 1.373 0.011 1.362 1.375 9  
N(2)=N(2) C#N=N—C# (cis) 1.245 1.244 0.009 1.239 1.252 21  
C#N=N—C# (trans) 1.222 1.222 0.006 1.218 1.227 6  
C#N=N—C# (overall) 1.240 1.241 0.012 1.230 1.251 27  
CarN=N—Car 1.255 1.253 0.016 1.247 1.262 13  
XN=N=N  (azides) 1.216 1.226 0.028 1.202 1.237 19  
N(2)=N(1) X—N=N=N (azides) 1.124 1.128 0.015 1.114 1.137 19  
N(3)—O(2) (C,H)2NOH (Nsp2: planar) 1.396 1.394 0.012 1.390 1.401 28  
C2NO—C (Nsp3: pyramidal) 1.463 1.465 0.012 1.457 1.468 22  
C2NO—C (Nsp2: planar) 1.397 1.394 0.011 1.388 1.409 12  
in furoxan (N2—O1) 1.438 1.436 0.009 1.430 1.447 14  
N(3)—O(1) (C[\ddb])2N+O in pyridine N-oxides 1.304 1.299 0.015 1.291 1.316 11  
in furoxan (+N2—O6) 1.234 1.234 0.008 1.228 1.240 14  
N(2)—O(2) in oximes:              
 (C#)2—C=NOH 1.416 1.418 0.006 1.416 1.420 7  
 (H)(Csp2)—C=NOH 1.390 1.390 0.011 1.380 1.401 20  
 (C#)(Csp2)—C=NOH 1.402 1.403 0.010 1.393 1.410 18  
 (Csp2)2—C=NOH 1.378 1.377 0.017 1.365 1.393 16  
 (C,H)2—C=NOH (overall) 1.394 1.395 0.018 1.379 1.408 67  
in furazan  (O1—N2, O1—N5) 1.385 1.383 0.013 1.378 1.392 12  
in furoxan  (O1—N5) 1.380 1.380 0.011 1.370 1.388 14  
in isoxazole (O1—N2) 1.425 1.425 0.010 1.417 1.434 9  
N(3)=O(1) in nitrate ions NO[^-_3] 1.239 1.240 0.020 1.227 1.251 105  
in nitro groups:              
 C*—NO2 1.212 1.214 0.012 1.206 1.221 84  
 C#NO2 1.210 1.210 0.011 1.203 1.218 251  
 CarNO2 1.217 1.218 0.011 1.211 1.215 1116  
 C—NO2 (overall) 1.218 1.219 0.013 1.210 1.226 1733  
N(3)—P(4) X2P(=X)—NX2 Nsp2: planar 1.652 1.651 0.024 1.634 1.670 205  
X2P(=X)—NX2 Nsp3: pyramidal 1.683 1.683 0.005 1.680 1.686 6  
X2P(=X)—NX2 (overall) 1.662 1.662 0.029 1.639 1.682 358  
subsets of this group are:              
 O2P(=S)—NX2 1.628 1.624 0.015 1.615 1.634 9  
 C—P(=S)—(NX2)2 1.691 1.694 0.018 1.678 1.703 28  
 O—P(=S)—(NX2)2 1.652 1.654 0.014 1.642 1.664 28  
 P(=O)—(NX2)3 1.663 1.668 0.026 1.640 1.679 78  
N(3)—P(3) NXP(—X)—NXP(—X)— (P2N2 ring) 1.730 1.721 0.017 1.716 1.748 20  
NXP(=S)—NXP(=S)— (P2N2 ring) 1.697 1.697 0.015 1.690 1.703 44  
in P-substituted phosphazenes:              
 (N[\ddb])2PN (amino) 1.637 1.638 0.014 1.625 1.651 16  
 (N[\ddb])2PN (aziridinyl) 1.672 1.674 0.010 1.665 1.676 15  
N(2)=P(4) Ph3P=N+=P—Ph3 1.571 1.573 0.013 1.563 1.580 66  
Ph3P=N—C,S 1.599 1.597 0.018 1.580 1.615 7  
N(2)[\ddb]P(3) N[\ddb]P aromatic in phosphazenes 1.582 1.582 0.019 1.571 1.594 126  
N[\ddb]P aromatic in P[\ddb]N[\ddb]S 1.604 1.606 0.009 1.594 1.612 36  
N(3)—S(4) C—SO2NH2 1.600 1.601 0.012 1.591 1.610 14 35
C—SO2NH—C# 1.633 1.633 0.019 1.615 1.652 47 35
C—SO2N—(C#)2 1.642 1.641 0.024 1.623 1.659 38 35
N(3)—S(2) C—SNX2 Nsp2: planar 1.710 1.707 0.019 1.698 1.722 22 23
(for Nsp3 pyramidal see MODIAZ: 1.765)              
XSNX2 Nsp2: planar 1.707 1.705 0.012 1.699 1.715 30 23
N(2)—S(2) C=NSX 1.656 1.663 0.027 1.632 1.677 36  
N(2)[\ddb]S(2) N[\ddb]S aromatic in P[\ddb]N[\ddb]S 1.560 1.558 0.011 1.554 1.563 37  
N(2)=S(2) N=S in N=S=N and N=S=S 1.541 1.546 0.022 1.521 1.558 37  
N(3)—Se see COJCUZ (1.830), DSEMOR10 (1.846, 1.852), MORTRS10 (1.841)              
N(2)—Se see SEBZQI (1.805), NAPSEZ10 (1.809, 1.820)              
N(2)=Se see CISMUM (1.790, 1.791)              
N(3)—Si(5) see DMESIP01, BOJLER, CASSAQ, CASYOK, CECXEN, CINTEY, CIPBUY, FMESIB, MNPSIL, PNPOSI (1.973–2.344)              
N(3)—Si(4) X3SiNX2 (overall) 1.748 1.746 0.022 1.735 1.757 170  
subsets of this group are:              
 X3SiNHX 1.714 1.719 0.014 1.702 1.727 16  
 X3SiNXSiX3 acyclic 1.743 1.744 0.016 1.731 1.755 45  
 NSiN in four-membered rings 1.742 1.742 0.009 1.735 1.748 53  
 NSiN in five-membered rings 1.741 1.742 0.019 1.726 1.749 33  
N(2)—Si(4) X3SiNSiX3 1.711 1.712 0.019 1.693 1.729 15  
N—Te see ACLTEP (2.402), BIBLAZ (1.980), CESSAU (2.023)              
O(2)—O(2) C*—OO—C*,H τ(OO) = 70–85° 1.464 1.464 0.009 1.458 1.472 12  
C*—OO—C*,H τ(OO) approx. 180° 1.482 1.480 0.005 1.478 1.486 5  
C*—OO—C*,H (overall) 1.469 1.471 0.012 1.461 1.478 17  
O=C—OO—C=O see ACBZPO01 (1.446), CEYLUN (1.452), CIMHIP (1.454)              
Si—OO—Si 1.496 1.499 0.005 1.490 1.499 10  
O(2)—P(5) XP—(OX)4             41
trigonal bipyramidal: axial 1.689 1.685 0.024 1.675 1.712 20  
trigonal bipyramidal: equatorial 1.619 1.622 0.024 1.604 1.628 20  
square pyramidal 1.662 1.661 0.020 1.649 1.673 28  
O(2)—P(4) C—OP([\ddb]O)[^{2-}_3] 1.621 1.622 0.007 1.615 1.628 12  
(H—O)2P([\ddb]O)[^-_2] 1.560 1.561 0.009 1.555 1.566 16  
(C—O)2P([\ddb]O)[^-_2] 1.608 1.607 0.013 1.599 1.615 16  
(C#O)3P=O 1.558 1.554 0.011 1.550 1.564 30  
(CarO)3P=O 1.587 1.588 0.014 1.572 1.599 19  
XOP(=O)—(C,N)2 1.590 1.585 0.016 1.577 1.601 33  
(XO)2P(=O)—(C,N) 1.571 1.572 0.013 1.563 1.579 70  
O(2)—P(3) (N[\ddb])2PO—C (N[\ddb]P aromatic) 1.573 1.573 0.011 1.563 1.584 16  
O(1)=P(4) C—O—P([\ddb]O)[^{2-}_3] (delocalized) 1.513 1.512 0.008 1.508 1.518 42  
(H—O)2P([\ddb]O)[^-_2] (delocalized) 1.503 1.503 0.005 1.499 1.508 16  
(C—O)2P([\ddb]O)[^-_2] (delocalized) 1.483 1.485 0.008 1.474 1.490 16  
(C—O)3P=O 1.449 1.448 0.007 1.446 1.452 18  
C3P=O 1.489 1.486 0.010 1.481 1.496 72  
N3P=O 1.461 1.462 0.014 1.449 1.470 26  
(C)2(N)—P=O 1.487 1.489 0.007 1.479 1.493 5  
(C,N)2(O)—P=O 1.467 1.465 0.007 1.462 1.472 33  
(C,N)(O)2P=O 1.457 1.458 0.009 1.454 1.462 35  
O(2)—S(4) C—OSO2—C 1.577 1.576 0.015 1.566 1.584 41  
C—OSO2—CH3 1.569 1.569 0.013 1.556 1.582 7  
C—OSO2—Car 1.580 1.578 0.015 1.571 1.588 27  
O(1)=S(4) C—SO2—C 1.436 1.437 0.010 1.431 1.442 316 42
XSO2—NX2 1.428 1.428 0.010 1.422 1.434 326  
C—SO2—N—(C,H)2 1.430 1.430 0.009 1.425 1.435 206  
C—SO2—O—C 1.423 1.423 0.008 1.418 1.428 82  
in SO[^{2-}_4] 1.472 1.473 0.013 1.463 1.481 104  
O(1)=S(3) C—S(=O)—C 1.497 1.498 0.013 1.489 1.505 90 5
O—Se see BAPPAJ, BIRGUE10, BIRHAL10, CXMSEO, DGLYSE, SPSEBU              
(1.597 for O=Se to 1.974 for O—Se)              
O(2)—Si(5) (XO)3Si—(N)(C) 1.663 1.658 0.023 1.650 1.665 21  
O(2)—Si(4) X3SiOX (overall) 1.631 1.630 0.022 1.617 1.646 191  
subsets of this group are:              
 X3SiO—C# 1.645 1.647 0.012 1.634 1.652 29  
 X3SiO—Si—X3 1.622 1.625 0.014 1.614 1.631 70  
 X3SiOOSiX3 1.680 1.676 0.008 1.673 1.688 10  
O(2)—Te(6) (XO)6Te 1.927 1.927 0.020 1.908 1.942 16  
O(2)—Te(4) (XO)2TeX2 2.133 2.136 0.054 2.078 2.177 12  
P(4)—P(4) X3PPX3 2.256 2.259 0.025 2.243 2.277 6  
P(4)—P(3) see CECHEX (2.197), COZPIQ (2.249)              
P(3)—P(3) X2PPX2 2.214 2.210 0.022 2.200 2.224 41  
P(4)=P(4) see BUTSUE (2.054)              
P(3)=P(3) see BALXOB (2.034)              
P(4)=S(1) C3P=S 1.954 1.952 0.005 1.950 1.957 13  
(N,O)2(C)—P=S 1.922 1.924 0.014 1.913 1.927 26  
(N,O)3P=S 1.913 1.914 0.014 1.906 1.921 50  
P(4)=Se(1) X3P=Se 2.093 2.099 0.019 2.075 2.108 12  
P(3)—Si(4) X2PSiX3: 3- and 4-rings excluded 2.264 2.260 0.019 2.249 2.283