History
The term was introduced in 1939 by Robert S. Mulliken in the course of his work on UV spectroscopy of conjugated molecules. Mulliken observed that on adding alkyl groups to alkenes the spectra shifted to longer wavelengths. This bathochromic shift is well known in regular conjugated compounds such as butadiene. He was also the first to attribute the lower heat of hydrogenation for these substituted compounds (compared to those without substitution) to hyperconjugation. An effect predating the 1939 hyperconjugation concept is the Baker–Nathan effect reported in 1935.
Read more about this topic: Hyperconjugation
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