Peter Buzek

Confirmation of the H-bridged structure of the 2-butyl cation by comparison of experimental and ab initio IR frequencies

The IR spectrum of the 2-butyl cation, measured at –125 °C in an SbF5 matrix and calculated ab initio(MP2(FULL)/6-31G*), is characterized by a C(H [graphic omitted] ) C peak at 2175 cm–1 assigned to the nonclassical H-bridged (C2-symmetry) structure 1.

Characteristic frequencies of hydrogen-bridged carbocations. IR spectra and ab initio calculations of the nonclassical structures of the cyclooctyl cation

The symmetrically H-bridged structure of the cyclooctyl cation is confirmed definitively by the characteristic IR vibration at 1845 cm–1 and by the agreement of the IGLO chemical shifts calculated with MP2/6-31G* geometry of the chair–boat (CS) conformation with the experimental NMR values.

Das Reaktionsverhalten der N-Basen NH3, NCNH2 und NCCN gegenüber EF5 und EF5/HF (E = As, Sb)

Abstract The reaction of ammonia, cyanamide and cyanogen with arsenic pentafluoride in liquid SO 2 led to the formation of the adducts NH 3 ·AsF 5 ( 1 ), H 2 NCN·AsF 5 ( 2 ) and NCCN·AsF 5 ( 3 ). Similarly, the compound NCCN·SbF 5 ( 4 ) was obtained from (CN) 2 and SbF 5 in sulfur dioxide solution. The adduct 1 was treated wit HF (excess) to give NH 4 + AsF 6 − in quantitative yield. Protonation of H 2 NCN and (CN) 2 with anhydrous HF in the presence of EF 5 (E=As, Sb) afforded the salts H 2 NCNH + AsF 6 − ( 5 ) and NCCNH + SbF 6 − ( 6 ), the latter being only stable in solution and existing in equilibrium with 4 ( 4 / 6 =4:1). Fluorination of 2 with elemental fluorine in C 2 F 4 Cl 2 solution (R-114) led to the formation of 3 , NH 4 + AsF 6 − and (presumably) NF 3 . In order to assign the vibrational spectra (Raman) of 3 and 4 , ab initio calculations were carried out on the HF/6-31G * theory level using NCCNH + as a model for 3 and 4 (H + as a Lewis acid instead of AsF 5 or SbF 5 , respectively).