π-electron acceptor/donor group
A
substituent
capable of a
+R
(e.g.
NO
2
) or
−R
(e.g.
OCH
3
) effect, respectively.
See:
electronic effect
,
polar effect
,
σ-constant
Source:
PAC, 1994,
66
, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1155