Etude par résonance magnétique nucléaire de composés organiques contenant des chalcogènes. I. L'anisole et ses analogues soufré, sélénié et tellure

Abstract

On rapporte Ics resultats d'une dtude par resonance magnctiquc du proton et du carbonc 13 sur l'anisole, le thioanisole, le selenoanisole et le telluroanisole, ainsi que sur certains de lcurs derives l~orrr substituCs. Considdres comnie des niethyles substitues, ccs composds ont iln coniportement analogue h celui des halogenurcs dc methyle. On a pu mettre cn evidence u n c relation lineairc entre le cleplacenient chiniiqile des protons et cclui du carbone du niethyle dans la serie de l'anisole et dans les halogenures de mcthyle h la fois. Si ces resultats s'interpretent le plus souvent i partir ci'cffcts electroniques, un "effet d'atomc Ioi~rd" doit Etre invoqud clans le cas dcs composes tellures. Les resultats experinientaux ne sont pas en desaccord avcc I'hypothese cl'une co~ifiguration plane des con~poses etudies. GABRIEL LLABRES, MARCEL BAIWIR, LLON CHRISTIAENS, JOSE DENOEL, L~O P O L D LAITEM, and JEAN-LOUIS PIETTE. Can. J. Cheni. 56,2008 (1978).Results are reported of a study by ' H and "C nuclear magnetic resonance of anisolc, thioanisole, selcnoanisole and telluroanisole as well as of several of their prrrrr-substituted derivntives. I F these compounds are considered as substituted methyl groups, they display a behavioiir analogous to that of the methyl halides. I t is possible to demonstrate that a linear relation cxists between the proton and the carbon chemical shifts in the anisole scries as well as in the methyl halides. Although these results most frequently are interpreted in terms of electronic effects, a 'heavy atom effcct' must be invoked for the telluriuni con~pounds. The experimental results do not contradict the hypothcsis that the colnpounds studied have a planar configuration [Journal translation]

The planar conformation of 2-methylthiobenzaldehyde in solution

“…The chemcial shift of the methyl protons in 1 is 2.45 ppm, is 2.44 ppm in thioanisole (25), and 2.43 ppm in 2,5-dichlorothioanisole (20). In contrast, it is 2.27 ppm in 2-hydroxythioanisole and, as shown previously (2 I), reflects the upfield shift caused by the magnetic anisotropy of the benzene nucleus in the perpendicular conformation.…”

“…Hence the TT electron densities at C-3 and C-5 in 1 should increase, reflecting the increased IT electron donation by SCH,. On an additive basis, the observed shifts in benzaldehyde (26) and thioanisole (25), together with SH as 7.25 for benzene in CC14, imply S,, 84, S5, and S6 as 7.36, 7.43, 7.24, and 7.70 respectively. The observed shifts display excess high field shifts of 0.08 and 0.04 ppm at H-3 and H-5, respectively, consistent with increased IT electron density at the sites ortho and p a r a to SCH3 and therefore with an increased tendency towards planarity of this substituent.…”

“…..rr conjugation in thioanisole and thiophenol is not very strong, the barrier to internal rotation about the C 1 -S bond being only about 3.3 kJ/mol (22,23). The ring proton shifts reflect the extent of conjugation and are the same for the two compounds to within 0.02 ppm (24,25). In 1 , the coplanar conformation of the SCH, group will be favored by the presence of the carbonyl function.…”

High Overtones of the C−H Stretching Vibrations in Anisole and Thioanisole

“…To evaluate the conjugation effect of the heteroatoms toward the aromatic ring, useful information can be obtained from the protonic magnetic resonance . This effect appears relevant in anisole, where the hydrogen atoms in ortho and para positions are more shielded (δ ortho = 6.749; δ meta = 7.145; δ para = 6.811).…”

Carbon-13 nuclear magnetic resonance studies of organotellurium compounds. II. Chemical shift trends

“…However, the available data on tellurium which corresponds to a decrease in the tellurium compounds are limited compared with polarity of the Te-C bond. ~a g n e t i c anisotropic those for sulphur and selenium (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). effects originating in the tellurium substituents are we have recently reported our studies on 1 3~ nmr not expected to vary much in this closely related spectra of phenyl and p-methoxyphenyl tellurium series; moreover, they are expected to be small (8).…”