Ethynyl and Cyano Cyclopropanes

The cyano group as a 71-acceptor substituent induces a shortening of the distal bond in the cyclopropyl ring. A mean asymmetry parameter = -0.017 (2) A has been found8. 

The structures of cyclopropylacetylene (92) and cyanocyclopropane (93) were studied in several laboratories within a few years. Parameters from the more recent experimental investigations are shown in Table 8. 

The molecular structure of 93 has been determined149 also by low-temperature XD at -85 °C (Table 8). The molecules are bisected by mirror planes in the orthorhombic Pnma crystal, and have no special intermolecular contacts. Uncorrected bond lengths are systematically smaller than the MW data, but curiously not for the C—C(=) single bond. 

The molecules of /rfl 5-l,2,3-tricyanocyclopropane (94t) also lie on mirror planes in the Puma crystal The C—C(N) and C=N bond lengths in solid 93,94t and in its cis isomer  

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