Bond length analysis

Table 2 Face-capping arenes used for bond length analysis...

Theoretical analysis of certain features in the electromagnetic spectrum yields basic molecular parameters such as bond lengths and bond stiffness. We shall see presently that the mechanical spectra can be related to molecular parameters and not just modelistic characteristics as we have used until now. 

The pyrimidine ring is virtually flat. Its corrected bond lengths, as determined by a least-squares analysis of the crystal structure data for a unit cell of four molecules, are shown in formula (2) (60AX80), and the bond angles derived from these data show good agreement with those (3) derived by other means (63JCS5893) for comparison, each bond... 

Interatomic distances calculated from the detailed analysis of rotational fine structure of the UV spectrum of pyrazine are in close agreement with those observed in (7) and (8), with the calculated bond lengths for C—C of 1.395, C—N 1.341 and C—H 1.085 A (60DIS(20)4291). Thermochemical data have provided a figure of 75 kJ moP for the delocalization energy of the pyrazine ring (B-67MI21400). 

X-ray analysis of diaziridinone (25) gave an N—N bond length of 1.60 A, and an N—CO bond length of 1.325 A. The bonds from nitrogen to substituent form angles of 56° with the plane of the ring the substituents are trans to each other (78JOC922). 

The triatomic cations X3+ are nonlinear and thus isostructural with other 20-electron species such as XY2+ (p. 839) and SCI2 (p. 689). The contrast in bond lengths and angles between I3+ (Fig. 17.15) and the linear 22-electron anion I3 (p. 836) is notable, as is its similarity with the isolectronic Tc3 anion (p. 764). Likewise, Br3Asp6 is isomorphous with I3ASF6 and the non-linear cation has Br Br 227.0 pm and an angle of 102.5° > (cf. Br3", Table 17.15). The structures of the penta-atomic cations Brs+ (2) and I5+ (3) have been determined by X-ray analysis of their AsFe salts and shown to have centrosymmetric Cjh symmetry like the... 

Apply the same analysis to trimethyloxonium ion, MesO" a cationic electrophile. Examine the LUMO. What are the best sites for nucleophile-LUMO overlap How would electron transfer affect CO bond lengths ... 

The X-ray crystal analysis of 5-trimethylsilanyl-4-trimethylsilanylethynyl-l//-pyrazole-3-carboxylic acid ethyl ester was obtained only with / = 0.17 because the crystals of the molecule diffracted extremely weakly and only a very limited data set was available. This means that although the gross stereochemistry of the molecule has been determined, individual bond lengths are not reliable (88JOM247). 

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