STRUCTURE OF THE MODEL GRIGNARD-TYPE REAGENT ClZnCH3 (~X1A1) BY MILLIMETER-WAVE SPECTROSCOPY

Pure rotational spectra of the (ClZnCH3)-Cl-37, ClZnCD3, and (ClZnCH3)-C- 13 isotopologues of monomeric ClZnCH3 ((X) over tilde (1)A(1)) have been recorded using millimeter-wave direct absorption techniques in the frequency range 263-303 GHz. These species were synthesized in the gas phase in a DC discharge by the reaction of zinc vapor, produced in a Broida-type oven, with (ClCH3)-Cl-37(in natural chlorine abundance), ClCD3, or (ClCH3)-C-13. Five to eight rotational transitions J + 1 -> J consisting of K ladder structure were measured for each iso- topologue, identifying all three species as prolate symmetric tops. The data for each isotopologue were analyzed with a symmetric top Hamiltonian and rotational and centrifugal constants determined. In combination with previous measurements of (ClZnCH3)-Zn-64, (ClZnCH3)-Zn-66, and (ClZnCH3)-Zn-68, an r(m)((2)) structure was determined for this organozinc compound. The bond lengths in ClZnCH3 were calculated to be r(Cl-Zn) = 2.0831(1) angstrom, r(Zn-C) = 1.9085(1) angstrom, and r(C-H) = 1.1806(5) angstrom, considerably different from those established from crystal structures of related species ClZnCH2CH3 and ClZnEtTMEDA. The H-C-H bond angle was found to be 110.5 degrees - slightly larger than that in methane. These data serve to benchmark future structure calculations of organozinc compounds, which are widely used in organic synthesis. (C) 2020 Elsevier Inc. All rights reserved.