Microwave Spectrum and Structure of Propynal (H–C≡C–CHO)

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Abstract
The moments of inertia IB0 and IC0 of fifteen isotopic species of propynal have been determined from the frequencies of certain lines in the type a spectra. With the aid of type b transitions, IA0 and the inertial defects Δ have been obtained for some of the isotopic species. Using equations relating the atomic coordinates to the change in the moments of inertia on isotopic substitution, three independent sets of molecular parameters have been obtained (two for C=O). The agreement between the three sets of data is within the probable experimental error. The mean values of the molecular parameters are as follows: rs(C–H) (acet.) = 1.0553A, rs(C–H) (ald.) = 1.1064A, rs(C≡C) = 1.2089A, rs(C–C) = 1.4446A, rs(C=O) = 1.2150A, ≰CCO = 123°47′, ≰CCC = 178°24′, ≰CCH (ald.) = 113°54′, ≰CCH (acet.) = 180°0′. The error in the bond lengths is estimated to be ±0.001 A, and in the angles ±10′. A slight deviation from linearity (1°36′±10′) was apparent in the carbon chain.