Geminal coupling constants in methylene groups—II

Exploiting a multicomponent domino reaction strategy for the tailoring of versatile environmentally sensitive fluorophore-based nicotinonitriles incorporating pyrene and fluorene moieties

“…It should be emphasized that the coupling constants ( 2 J HH ) in the CH 2 group (ranging from −21.5 to −35.5 and −19.0 to −24.0 Hz, respectively) show some variations and unusually higher absolute values. This observation may be concisely elucidated based on the following two facts: (a) the 2 J HH coupling constant becomes more negative when a CH 2 group is attached to a π-acceptor such as carbonyl, imino, or cyano group or conjugated with aryl, alkene and alkyne substituents, as the H–C–H angle is decreased and 2 J HH coupling constant becomes more negative (larger); 45 and (b) the negative mesomeric effect of the cyano group attached to the pyridine ring decreases the electron density especially at the 2-position, and sequentially, it may act as a π-acceptor group.…”

NMR Experiments on Acetals. Part 28. 1,3‐Dioxanes with Non‐Chair Conformations and the 2J(Och2O) Criterium

“…The bornano-dioxanes are quite satisfying models for classical boat forms having one of the oxygen atoms in the bowsprit (see Chart I, ( 5 ) and (6)). The ring-junction holds the dioxanic part at that bond firmly stiff, with a torsion ring angle of almost 0".…”

“…Structure--2J(2) J(4,5) 6H-4 6H-6 6H-2e 6H-2a (QFi, assignment (cps) (CPS) (ppm) (ppm) (ppm) b p m ) Chrom C ) ( The relative small values for 3J (4,5) In (1) and (2) (resp. 2.0 and 3.5 cps*) show 173 that the H-atoms involved, are cis to each other, and the smallest value must correspond to 3J(4a, 5e) (cis A : B junction), while 3.5 cps fits fairly well with 3J(4e, 5a), although it is somewhat small [7].…”

Conformational Study of N-Methyl-5,6-dihydro-7H,12H-dibenz[c,f]-azocine by Nuclear Magnetic Resonance Spectroscopy

“…It is recognized that a benzene ring on a methylene group causes a negative shift on the geminal proton-proton coupling constant and that this shift varies with conformation. Empirical (29,30) and theoretical (31, 32) evidence support this correlation and estimate the effect to be at least 4 Hz in the most favorable conformation 5 and zero in the conformation 6, achieved by a rotation of 90" about the phenyl-CH, bond. A Dreiding model of the crown form of 3 shows 4 to be very close to 90" for both benzene rings, leading to the expectation that they should have a negligible influence on 2J.…”