Microwave spectrum of monohalogenated allenes: bromoallene

Abstract

The microwave spectrum of bromoallene for ⁷⁹Br and ⁸¹Br species has been studied from 15 to 35 GHz. A least-squares analysis of the observed a- and b-type transition frequencies gave rotational, quartic centrifugal distortion constants and the components of the nuclear quadrupole coupling constants tensor in the principal axes system: A= 27 849.952 (63), B= 2009.8672 (40) and C= 1897.3682 (27) MHz, D_J= 0.705 (25), D_JK=–46.1 (10), δ_J= 0.0915 (29) kHz, χ_aa= 377.11 (94), χ_bb–χ_cc= 182.78 (13) and |χ_ab|= 381.32 (24) MHz for ⁷⁹Br species; and A= 27 820.459 (52), B= 1996.0270 (33) and C= 1884.8908 (22) MHz D_J= 0.632 (21), D_JK=–46.5 (8), δ_J= 0.0931 (16) kHz, χ_aa–χ_cc= 152.42 (10) and |χ_ab|= 318.00 (16) MHz for ¹⁸Br species. The structural parameters are calculated from the observed rotational constants. The bond length C—Br in bromoallene was found to be longer than that in bromoethene, in accordance with lower π character for C—Br in bromoallene than in bromoethene.