C-X bonds lengths

Table 5 Comparison of C—X Bond Lengths for Parent Heterocycles and their Dibenzo Derivatives...

For the antiaromatic three-membered heterocycles, experimental data are available only for thiirenes (and there is some doubt about the true antiaromaticity of thiirenes). Bond lengths have been calculated, however, for these antiaromatic 47r-systems (80PAC1623). In comparison with the corresponding saturated heterocycles, the C—X bond lengths are increased by 0.05 to 0.17 A and the C—C bond length is decreased by 0.2 A. 

Using the carbon atom covalent radius 0.77 A and the covalent radii given in Figure 19-3, predict the C—X bond length in each of the following molecules CF<, CBr4, CI4. Compare your calculated bond lengths with the experimental values C—F in CF4 = 1.32 A, C—Br in CBr = 1.94 A, C—I in CI4 = 2.15 A. 

The size of the halogen atom increases going down the periodic table => the C-X bond length increases going down the periodic table. 

Table 10.2 Carbon-Halogen (C— X) Bond Lengths, Bond Enthalpies and Dipole Moments...

The relationship between secondary a.-1 H/2H KIEs and transition state looseness has been investigated by MP2/6-31 ++G(d,p) calculations on three identity X- + CH3X 5k2 reactions.69 The secondary KIE increases with increasing transition structure looseness. It was shown that looseness is best defined as a A-elongation of the C—X bond lengths, where the reference state can be either the isolated reactants or the ion-dipole complex. 

TABLE 4. Relation between C—X bond lengths and racemization barriers for compounds 17a-17c and 17e85... 

None of the three levels consistently over- or underestimates C-C bond lengths. HF/6-31G C-X (X = O, N, Cl, S) bond lengths tend to be underestimated slightly (ca. 0.015 A) while MP2/6-31G C-X bond lengths may tend to be slightly (ca. 0.01 A) overestimated. HF/3-21G 1 C-X bond lengths are not consistently over- or underestimated. 

M—C and C—X Bond Lengths and M—C—X Bond Angles of some Halogenoalkyl Transition Metal Complexes... 

Complex M—C bond length (pm) C—X bond length (pm) M—C—X bond angle O Ref. 

Table 6 Comparison of C—X bond lengths for dibenzo heterocycles 119 and parent ring...

Table 3.11 Transition temperatures (°C), C-X bond length (A), dipole moment of C-X bond (Debye) birefringence (20°C), s...

Carbonyl halides and thiocarbonyl halides. All the compounds COCl2/ and COBr2/ have been studied in the vapour state by e.d. and/or m.w., and COCI2 (phosgene) has also been studied in the crystalline state/ The C-X bond lengths are close to the values expected for single bonds, while the C=0... 

There appears to be some sort of weak covalent bonding between X and N atoms of adjacent molecules, the effect being most marked in the iodide, where the intermolecular I-N distance is only 2-8 A, far less than the sum of the van der Waals radii (see p. 232). The C—X bond lengths within the molecules are appreciably less than the single-bond values in the molecules CX4 and are the same as in H3C—C=C—X, but C N is very close to the value in HCN. 

Case 1 is represented by F3C—X, F2C=X, or FC X, where X is N, C, O, or a halogen, but not an atom which is double-bonded to an adjacent atom. Here the substitution of fluorine for hydrogen decreases the C—X bond length, with one notable exception, perflu-oroethane, where the C—C distance is slightly larger (r = 1.545 0.006 com-... 

In the following tables we assembled data on the X-COR compounds and categorized C—X bond lengths in terms of an interaction between function groups . (-X and -COR), as was done for the CF3—X sequence. But instead of focusing attention on RC—X vs... 

However, the overlap between the p-orbitals of the heteroatom and ring carbons depends also upon the C—X bond length and the disparity between the size of the orbitals. From this point of view, the overlap should be maximum in the case of oxygen, and the ability to conjugate should be in the order O > S > Se > Te. The observed order of ground-state aromaticity (with a maximum for the thiophene ring) is the result of the interplay of these opposing factors. 

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