cyano groups were found to be slightly smaller than a phenyl ring. In contrast, vinyl and, in particular, formyl groups proved to be larger than phenyl. The latter difference is due to the loss of conjugation forces at the planar transition state. α-Hydroxyhexafluoroisopropyl is slightly more bulky than tert-butyl. Pentafluorophenyl and trifluoromethoxy exhibit nearly the same effectivesize as phenyl
Someone who says “A” should be prepared to also say “B”: In contrast to cyclohexane model‐based A values, biphenyl model‐derived B values are powerful tools to quantify steric repulsion in and conformational behavior of ortho‐substituted aromatic compounds.