Microwave studies of 4-methyl-1-pentyne

The gas-phase structures of 4-methyl-1-pentyne have been characterized by microwave spectroscopy, supplemented by ab initio calculations. Cs and C1 conformers are identified and assigned. These structures exhibit approximately equal energies, although the C1 is twice as abundant by virtue of degenerate forms. Both conformers display evidence of stabilizing γ-CH/π interactions. Computationally, this stability is only seen if electron correlation is explicitly included in the model. A small energetic benefit is calculated for the interaction of a second γ-hydrogen atom with one triple bond.