We report the detection of the acetylene derivative propynal (HC triple bond CCHO) in the cold cloud TMC-1, with an abundance that is very close to that for the related species tricarbon monoxide (C3O). Propadienone, an isomer of propynal with the formula H2C=C=C=O, was not detected and is hence less abundant than either C3O or HC2CHO.

The 211~212 transition of acetaldehyde at 3195·167 MHz has been observed in emission in SgrB2 with the Parkes 64 m telescope. Comparison of the intensities of the llO~ 111 and 211 ~212 emission lines suggests that both transitions may be inverted.

We report the measurement of three new lines of C3O in TMC-1. The observed peak antenna temperatures, appropriately corrected for atmospheric and telescope losses, are found to be consistent with a large velocity gradient radiative transfer model whose parameters span the range of standard values for this cloud. The derived fractional abundance for C3O is 1.4 x 10(-10), comparable with the results predicted from a model calculation based on a gas-phase ion-molecule reaction scheme. The results of negative searches for C3O in six other sources are not inconsistent with expected conditions in these clouds.

The self-consistent field molecular-orbital method, including adjustment of coulomb and resonance integrals using spectroscopic data, is applied to conjugated heterocyclic systems with the further elaboration that the effective nuclear charge for each 2pn-orbital is varied according to the electron density around the corresponding nucleus. Since the effective nuclear charge is a measure of the electronegativity of the 2pnorbita1, the method has been termed the " self-consistent electronegativity " (s.c.e.) method. The formaldehyde molecule has been studied to illustrate the new method.Calculations of spectroscopic intervals, already successfully achieved for heterocycles using fixed nuclcar cliarges, are little altered, but the calculated r-electron distribution is much more uniform than has been found in previous calculations on heterocycles.The dipole moment of formaldehyde can be accounted for entirely in terms of hybridization moments plus a small n-electron moment; no polarization of the C-0 a-bond need be invoked. The assumption of an unpolarized a-core, made in the present calculations, thus seems more reasonable than is widely believed. It is emphasized that an appreciablc portion of the molecular dipole in some hydrogen compounds may arise from hybridization of the hydrogen valence orbital.The oxygen lone-pair ionization potential cannot be explained merely in terms of the charge gained by the oxygen through carbonyl bond polarization. The present results suggest the values a 0 = a + O*lp and pco = 1.13p for the simple 111.0. method when applied to carbonyl compounds.

The relative rates of protodeboronation of benzene-, thiophen-2-, and thiophen-3-boronic acids at 70� determined by an extrapolation procedure, are 1 : 7.1 x 103 : 8.5 x 105. The relative reactivity for 2-substitution thus exceeds that found for any other electrophilic substitution of thiophen.