Triple-bond radii

In Table VI3) and Fig. 3 there are given radii for use in compounds of this type. The sum of the singlebond radii for two atoms gives the expected distance between these two atoms in such a compound when they are connected by a covalent bond. The sum of their double-bond or triple-bond radii similarly gives the expected distance when they are connected by a double or a triple bond. 

It seems probable also that, to within one or two percent, doublebond and triple-bond radii for various atoms should bear constant ratios to single-bond radii. We have chosen 0.79 for the triple-bond factor, which gives agreement with the observed distance in the N2 molecule, and 0.90 for the double-bond factor. The radii given in Table VI are obtained with these factors. 

Revised Values of Double-Bond Covalent Radii.—This investigation has led to the value 1.34 A. for the carbon-carbon double-bond distance, 0.04 A. less than the value provided by the table of covalent radii.111 4 Five years ago, when this table was extended to multiple bonds, there were few reliable experimental data on which the selected values for double-bond and triple-bond radii could be based. The single-bond radii were obtained -from the study of a large number of interatomic distances found experimentally by crystal-structure and spectroscopic methods. The spectroscopic value of the triple-bond radius of nitrogen (in N2) was found to bear the ratio 0.79 to the single-bond radius, and this ratio was as-... 

Table 2.2 Single, Double, and Triple Bond Radii (pm)...

Some other values of double-bond and triple-bond radii given in Table 7-2 have been obtained from experimental values of interatomic distances, and some have been estimated. In general the double-bond... 

A second point which must be made is that bond length depends upon bond number triple bonds are shorter than double bonds, which in their turn are shorter than single bonds. For this reason separate radii are required for these three types of bond, and it will be seen from the values given in table 4.03 that triple-bond radii are about 0-17 A less and double-bond radii about o io A less than the corresponding singlebond radii. We must, however, also remember that a bond will not necessarily have an integral bond number and that this number may be fractional if the bond involves resonance. Thus in benzene the C-C... 

Multiple-bond radii can also be obtained. For example, the triple-bond radii of carbon and nitrogen can be calculated from the bond lengths in HC=CH and N=N as 0.60 and 0.55, giving 1.15 for C=Nas compared with experimental values of 1.16. It may be stated, as a general rule, that the higher the order of a bond between two atoms, the shorter it is. Thus, for carbon—carbon bonds the following are typical lengths C—C, 1.54 C=C, 1.33 C=C, 1.21. 

Element Single-bond radius, pm Double-bond radius, pm Triple-bond radius, pm... 

In the course of the work it was found that the value assumed five years ago for the carbon double-bond covalent radius (obtained by linear interpolation between the single-bond and the triple-bond radius) is 0.02 A. too large in consequence of this we have been led to revise the double-bond radii of other atoms also. 

Double bond radius Triple bond radius... 

In the discussion of metallic radii we may make a choice between two immediate alternative procedures. The first, which I shall adopt, is to consider the dependence of the radius on the type of the bond, defined as the number (which may be fractional) of shared electron pairs involved (corresponding to the single, double, and triple bonds in ordinary covalent molecules and crystals), and then to consider separately the effect of resonance in stabilizing the crystal and decreasing the interatomic distance. This procedure is similar to that which we have used in the discussion of interatomic distances in resonating molecules.7 The alternative procedure would be to assign to each bond a number, the bond order, to represent the strength of the bond with inclusion of the resonance effect as well as of the bond type.8... 

In acetylene and hydrogen cyanide the length of the C—H bond is about 0.04 A less than it is for methane and its saturated derivatives, and we conclude that the correction to the effective radius of a carbon atom forming a triple bond is —0.040 A, twice as great as the double-... 

The cyanide ion is isoelectronic see Isoelectronic) with CO, N2 and NO+, with an electronic configuration of (la) (2a)2(3a) (4cr) (l7r)" (5a) this corresponds to a triple bond (one a-bond see a-Bond) and two tt-bonds see n-Bond)) between the carbon and nitrogen atoms. A lone pair see Lone Pair) of electrons is present on both atoms in CN. Calculations have indicated that the negative charge of the cyanide ion is shared approximately equally between the two atoms. The carbon-nitrogen triple bond distance is 1.16 A in the free cyanide ion the fundamental vibrational frequency of the C N bond (aqueous solution) is 2080 cm. The effective Crystallographic Radius of CN, as determined in cubic alkali metal cyanides, is 1.92 A this value is intermediate between those of chloride and bromide. 

Interestingly, the reactivity pattern in rare-earth metal-catalyzed hydroamination/cyclization reactions of aminoalkynes with respect to ionic radius size and steric demand of the ancillary ligand follows the opposite trend to that observed for aminoalkenes, namely decreasing rates of cyclization with increasing ionic radius of the rare-earth metal and more open coordination sphere around the metal. This phenomenon can be explained by a negligible sterical sensitivity of a sterically less encumbered triple bond, as sterically less open complexes and smaller metal ions provide more efficient reagent approach distances and charge buildup patterns in the transition state [110]. 

The P2 molecule has a triple bond, which is composed of one sigma bond and two pi bonds. The pi bonds are formed by sideways overlap of hp orbitals. Because the atomic radius of P is larger than that of N, the overlap is not as extensive as that in the N2 molecule. Consequently, the P2 molecule is much less stable than N2 and also less stable than P4, which contains only sigma bonds. 

The shortening of the bonds next to the triple bonds arises from the change of atomic radius of carbon when sp hybridised instead of sp hybridised. The acetylenic sides of the molecule are slightly hent, the inner angles at the sp atoms being 176-2 . 

Note that since we do not have the covalent radius for a triple-bonded O, we simply write the CO distance as being smaller than 1.17 A (i.e., < 1.17 A), which... 

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