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Substituent‐induced chemical shifts along CC double bonds
Author(s) -
Knorr Rudolf,
von Roman Therese,
Freudenreich Johannes,
Hoang Thi Phung,
Mehlstäubl Johann,
Böhrer Petra,
Stephenson David S.,
Huber Helmut,
Schubert Bernhard
Publication year - 1993
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260310608
Subject(s) - chemistry , substituent , chemical shift , moiety , double bond , coupling constant , medicinal chemistry , stereochemistry , olefin fiber , computational chemistry , organic chemistry , physics , particle physics , polymer
1 H and 13 C NMR signals were assigned and CH coupling constants ( 1 J , 2 J , 3 J ) determined for a series of α‐mono‐and α,α‐disubstituted (1,1,3,3‐tetramethyl‐2‐indanylidene)methanes with the following α‐substituents: (mesityl) 2 B, n ‐propyl, phenyl, tert ‐butyl‐C(NH), cyano, ( tert ‐butyl) 2 C(OH), pivaloyl, H 2 N‐CO, PhNH‐CO, carboxy, ritro, acetoxy, Me 3 SiO, Me 3 Si, PhS, PhSMe + , PhSO, PhSO 2 , bromo and trimethylstannyl. The 1 J couplings with the olefinic proton span the range 124.3–193.7 Hz. Substituent‐induced chemical shifts (SCS) of most of the nuclei with respect to the α‐unsubstituted olefin obey simple additivity in the α,α‐disubstituted compounds and are very similar to the SCS values along the CN double bond in the isoelectronic (1,1,3,3‐tetramethyl‐2‐indanylidene)amines within the error limits. The exceptions concern nuclei in the immediate vicinity of the perturbing substituent. A dominant mechanistic contribution of electric field effects appears likely for the more distant aromatic part of the indanylidene moiety. The chemical shifts of two (2,2,5,5‐tetramethylcyclopentylidene)methanes are shown to be compatible with the SCS parameters from the indanylidene series.