Hydrogen single bond distance

In the 1,2,3-triaminoguanidine (CHsNg)7 one C—N bond is particularly short (1.292 A) while all other bond distances are comparable to the typical lengths of the C—N and N—N single bond distances. The structure consists of sheets of TAG oriented in the direction along the direction of the b axis and held together by molecular forces and hydrogen bonds. 

The Lewis formula for ozone, however, is inconsistent with the experimentally determined structure. On the basis of the Lewis formula, we would expect ozone to have two different O—O bond lengths, one of them similar to the O—O single bond distance of 147 pm in hydrogen peroxide (HO—OH) and the other similar to the 121 pm O—O double bond distance in O2. In fact, both bond distances are the same (128 pm)— somewhat shorter than a single bond, somewhat longer than a double bond. The structure... 

The last of these complexes was identified through the X-ray diffi action determination of the structure of the salt K2ReH9 the nine hydrogen atoms are at the single-bond distance from the rhenium (6). 

Figure 10.2.6. Special distance measures for the characterization of proton environments a) distance r and angle a, to double bonds b) distance and angle Oc, to single bonds c) dihedral angle a, to the third bond from the hydrogen atom.

Two Tq values are given for each MM+ bond, and rg . If rg is available (has a non-zero value in the parameter file) then it is used in preference to the normal for bonds where atom i and atom j have at least two hydrogen atoms directly attached to them. For example, CH2-CH2, CH2-CH3, or CH3-CH3 bonds may have their own equilibrium distance differentiated from the average single bond between carbon atoms. 

The new carbon-carbon double-bond distance corresponds to the value 0.87 for the double-bond factor. Moreover, there are now available three accurately known triple-bond distances 1.204 for C=C in acetylene, 1.154 A. for C=N in hydrogen cyanide, and 1.094 for N==N in the nitrogen molecule, whereas five years ago only the last was known. The ratios of these distances to the corresponding sums of single-bond radii are 0.782, 0.785, and 0.781, respectively. We accordingly now select 0.78 as the value of the triple-bond factor. Revised covalent radii26 for first-row atoms are given in Table XV. 

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