A precise analysis of the ¹H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane. Ring pucker, signs of long-range J(H,H), internal rotational barrier, and van der Waals shifts

Abstract

. Can. J. Chem. 72, 1722Chem. 72, (1994. The 'H nuclear magnetic resonance spectrum of 2-phenyl-l,3-dithiane, as a dilute solution in a CS2-C6D12-TMS solvent mixture at 300 K, is analyzed to yield 8 chemical shifts and 22 distinct coupling constants, "J(H,H), n = 2-6. The coupling constant between H-2 and the para proton indicates, first, that the bisected conformer (phenyl plane perpendicular to the pseudo plane of the dithiane ring) is most stable and, second, that the apparent twofold barrier to rotation about the ~s p~--~s p~ bond is 9.6 kJ/ mol. The AMI, STO-3G, and STO-3G* computations confirm the twofoldedness of the barrier; the AM1 barrier is 9.4 kJ/mol.The empirical equation, 3~(~,~) = 13.36 cos2 + + 9.59 cos + -0.43, reproduces the vicinal coupling constants of the CH2CH2CH2 fragments and implies puckering angles +, , , +, , , and +, , of 54", 61°, and 64", respectively. It is implied that 3~ at + = 0" is larger than at + = 180". This results is discussed in terms of the latest theoretical approach to 3~ in the HCCH fragment.The 4~(~,~) signs and magnitudes for the CH2CH2CH2 fragment agree reasonably well with theory. For the CH2SCH fragment, 4~(~,~) values are positive, in contrast to corresponding numbers in the propanic fragment, perhaps the first experimental values for certain rigid orientations about a heteroatom. INDO MO FFT computations on propane, dimethyl ether, and dimethyl sulfide confirm the experimental trend in 4~(~,~) . 'J(H,H) and 'J(H,H) values are compared to those in related molecules. The striking differential shifts of the axial and equatorial protons are attributed to differential van der Waals interactions with the 3p lone-pair orbital on sulfur. A comparison of the ring proton chemical shifts with those in phenylcyclohexane and isopropylbenzene implies that C-S bonds are weaker net electron donors by hyperconjugation than are C-C bonds. It is also proposed that the ortho protons are deshielded by intramolecular van der Waals interactions with the 3p orbitals on the sulfur atoms.-TED SCHAEFER, JEREMY P. KUNKEL, ROBERT W.J SCHURKO et GUY M. BERNARD Can. J. Chem. 72, 1722Chem. 72, (1994. Le spectre rCsonance magnCtique nucltaire du 'H du 2-phCnyl-l,3-dithiane, dCterminC B 300 K, en solution diluCe dans un milange de solvants form6 de CS,, de C6D12 et de TMS, a Ct C analysi et on en a dtduit 8 dkplacements chimiques et 22 constantes de couplage distinctes, "J(H,H), n = 2 -6. La constante de couplage entre le proton H-2 et le proton en para indique, en premier lieu, que le conformkre avec bissection (dans lequel le plan du phCnyle est perpendiculaire au pseudo plan du noyau dithiane) est le plus stable et, deuxikmement, que la barrikre binaire apparente a la rotation autour de la liaison Csp2-Csp3 est de 9,6 kJlmol. Des calculs AM1, STO-3G et STO-3G* confirment que la barrikre est binaire; les calculs AM 1 indiquent que la barrikre est de 9,4 kJ/mol. L'Cquation empirique, 3~(~,~) = 13,36 cos2 + + 0,519 cos + -0,43, permet de reproduire les constantes de couplage vicinales du fr...

A Density Functional Study of 2-Lithio-1,3-dithiane and 2-Lithio-2-phenyl-1,3-dithiane: Conformational Preference of the C−Li Bond and Structural Analysis

“…The calculated minimum energy conformations for 2 -ax and 2 -eq show the phenyl ring perpendicular to the plane that bisects the 1,3-dithiane ring in the axial isomer, but aligned in the bisecting plane in 2 -eq (Figure ). This result is also in agreement with previous conformational studies in analogous systems 3 NBO population analysis of 2-phenyl-1,3-dithiane ( 2 ) and its lithiated derivatives at the Becke3LYP/6-31G( d,p ) level. …”

Experimental and theoretical investigation of NMR 2JHH coupling constant on six‐membered ring systems containing oxygen or sulfur atoms

“…24 An opposite behavior, i.e. an algebraic decrease of 2 J HH coupling was observed for 2-phenyl-1,3-dithiane, 25 namely 2 J HH D 13.99 Hz, which is more negative than that observed for cyclohexane 13.05 Hz , and such an algebraic decrease was ascribed to a hyperconjugative interaction of C-H bonds with sulfur-3p orbitals. However, it must be stressed that these interactions are not the only factors defining the magnitude of 2 J HH couplings.…”

Oxidative ring contraction of 2-phenyl-1,3-dithiane in ZSM-5: restricted mobility of 1,2-dithiolane radical cations in zeolite channels

“…30°. 19 Oxidation of 2 results in a subtle structure change; the sulfur lone pairs (and the S-CH 2 bonds) in 2 •+ become eclipsed, facilitating the delocalization of spin and charge between the sulfur centers. The planar arrangement of the CH 2 -S-S-CH 2 segment forces the bridging methylene group out of plane; a planar structure is a low-lying transition state between two equivalent 'envelope' conformers.…”