Bond energies from spectra

The structure of decaborane(16) 200> reveals that it should be considered as an apically substituted derivative of pentaborane(9). The bond energy of the unique boron-boron bond which connects the two B5H8 cages has been determined to be 3.2 0.2 e.v. from mass spectrometry 201> the standard heat of formation is 34.8 kcal. per mole 202>. An analysis of the vibrational spectrum of decaborane(16) has been made by Pinson and Lin 203> who note the absence of the strong absorption at 901 cm-1 which was previously reported 204>. 

Interatomic distances as calculated from the analysis of the rotational fine structure of the ultraviolet spectrum are C-C, 1.395 A C-N, 1.341A and C-H, 1.085 A.66 These are very similar to the bond lengths for pyridine which are C-2-C-3, 1.3945 A C-3-C-4, 1.3944 A and C-2-N, 1.3402 A. The C-N-C bond angle in pyrazine is 115° and the C-C-N bond angle 122.5°.56,67 A delocalization energy for pyrazine of ca. 18 kcal/mole is indicated from heats of combustion data.68 The C=N bond energy in 2,2,5,5-tetramethyl-2,5-dihydropyrazine has been calculated to be 130.3 kcal.58a... 

---