MICROWAVE SPECTRUM OF CYCLOPROPYL BROMIDE

The microwave spectra of four isotopic species of cyclopropyl bromide, namely C3H579Br, C3H 581Br, C3H4D79Br, and C3H4D81Br have been analyzed in the frequency region of 19000-31000 Mc/sec. The rotational constants obtained are as follows (given in megacycles per second) : A B C C3H5 79Br 16 504.9±65 2579.87±0.03 2457.68±0.03 C3H581Br 16 239.6±160 2560.49±0.03 2440.12±0.03 C3H4D 79Br 15 139.2±79 2S27.52±0.04 2455.93±0.05 C3H4D81Br 15 046.8±184 2502.84±0.05 2430.73±0.04 Two structures compatible with these data have been obtained for this molecule. Structure I was calculated by assuming for the hydrogen parameters values obtained for cyclopropyl chloride, whereas Structure II was derived with the assumption that all d C-H= 1.080 A and the ZH-C-H's are bisected by the ring. Structure I Assumed Calculated d C-H (trans) : 1.086 Å d C1-C2: 1.521±0.004 Å d C-H(cis) : 1.074 Å d C1-C3: 1.512±0.007 Å d C-H(sec) : 1.078 Å d C3-Br: 1.905±0.007 Å ∠C2-C1-H(m) : 116°50' /H(sec)-C3-Br: 116°±50′ ∠C2-C1-H ∠C2-C3-Br: 118°54'±1.0° Structure I Assumed Calculated d C-H: 1.080 Å d C1-C2: 1.518 ± 0.004 Å ∠C2-C1-H(cis): 117°37° d C1-C3: 1.507±0.010 Å ∠ C 2-C1-H(cis) : 117°37° d C3-Br: 1.899±O.OO5 Å ∠C3-C1-H(trans) : 117°6 ZH(sec)-C3-Br: 115°15±50̊ ∠H(cis)-C 1HO(trans) : 116°/C2-C3-Br: 119°30'±1.0° The analysis of the hyperfine structures of the spectra gives the following quadrupole coupling constants. For C 3W579 = 462.3±3.5 Me/sec, =-0.23±0.04; C3H581Br eCy = 391.2±1.0 Mc/sec, = 0.20± 0.02 ; C3H4DB = 451.0± 14 Mc/sec=-0.24±0.12; CÄD-4B r eQqm = 404.1 ±4 Mc/sec, T, = - 0.08± 0.10. The ionicity of the bond was estimated to approximately 22%.