Attractive nonbonded interactions. The solution conformation of N-(1-phenyl-2-propyl)nicotinamide chloride

Abstract

PFP PM 2 H H a M E S O -5 Figure 1. Conformations of 1,2-bis(pentafluorophenyl)-l,2-bis-(p-methoxypheny1)ethane. PMP = p-methoxyphenyl; PFP = perfluorophenyl.were prepared and analyzed.(Pentafluorophenyl)(p-methoxypheny1)methanol was coupled in the presence of chromium(I1) chloride to yield an equimolar (by NMR analysis) mixture of the diastereomeric 1,2-bis(p-methoxyphenyl)-1,2-bis(pentafluoro-pheny1)ethanes (meso-and dZ-5).15 The separation of the diastereomers was readily accomplished by successive crystallizations. In CDC1, one diastereomer exhibited the ethano methine proton resonance at 5.55 ppm while the second diastereomer's methine resonance appeared at 5.35 ppm; the respective melting points of the compounds are 199-202 "C and 140-143 OC. Employing the arguments advanced by Huang et al.,16J7 the higher melting diastereomer is tentatively assigned the meso configuration.18If polar interactions were to govern the conformations of meso-5, it would be expected that the preferred conformation of meso-5 would be 5a ( Figure 1); there exists in this conformation two pairs of attractive interactions (pentafluorophenyl-p-methoxyphenyl), while in conformers 5b and 5c two pairs of repulsive interactions exist with only a single attractive interaction. For dl-5, conformer 5a exhibits two pairs of repulsive interactions while both 5b and 5c exhibit two attractive and one repulsive interaction each. Assuming that the repulsive interaction between pentafluorophenyl groups would exceed that of p-methoxyphenyl groups, the preferred conformer of dl-5 would be 5c.Nuclear magnetic resonance analysis of the two diastereomers was conducted at 300 MHz employing the 13C satellite method., In CCll solution the 5.55 ppm diastereomer (meso) has 3&H = 13.25 f 0.15 Hz while the 5.35-ppm diastereomer (dl) has ,JHH = 12.65 f 0.05 Hz.It is clear that both diastereomers exist predominantly in the H-H anti conformation and that the anticipated ring-ring interactions do not, in this case, overcome the repulsive steric interactions encountered in H-H gauche conformations. It should be noted, however, that the coupling constants observed are in agreement with the tentative configurational assignments, i.e., the meso diastereomer should prefer the H-H anti conformation to a greater extent than the dl diastereomer with a resultant greater vicinal coupling constant. Experimental Section(Pentafluorophenyl)(p-methoxypheny1)methanol was prepared by the addition of 5.44 g (0.04 mol) of p-anisaldehyde (15) The coupling reaction is analogous to one reported previously by Finnoccharo et al. (Finnacchario, P.; Gust, G.; Hounshell, W. D.; Hummel, J.; Maravigna, P.; Mislow, K. (18) See, however, the caveat and exception listed in ref 8. 0022-3263/85/1950-1314$01.50/0to the Grignard reagent prepared from 12.35 g (0.05 mol) of bromopentafluorobenzene and 1.22 g (0.05 mol) of Mg turnings in 70 mL of anhydrous ether. Stirring was continued for 2 h after the addition was completed. The reaction mixture was cooled in an ice bath and the reaction was quenched...

Theoretical Study and X-ray Determination of Bianthrones: Long C−C Bond Length and Preferred Gauche Conformation

“…This energy profile is similar to that of H-bia . As the energy of the 0° conformation is significantly higher than the 120° conformation (Table ), the conformation interconversion should be achieved by a gauche ⇌ anti ⇌ gauche process, rather than a direct gauche ⇌ gauche process; this is also observed in the conformation interconversion of tetraalkylethanes 5b. In the gauche conformation of Model-1 , the C(sp 3 )−C(sp 3 ) bond length is 1.581 Å and the six-membered ring is nearly planar (flipping angle is 1°).…”

“…The conformations of substituted ethanes have been studied for a long time to understand the role of substituents in controlling the relative stability of gauche and anti forms. − In general, 1,1,2,2-tetraalkylethanes prefer the gauche conformation, whereas 1,1,2,2-tetraarylethanes, such as 1,1,2,2-tetraphenylthanes (e.g. 6 ), prefer the anti conformation 4a.…”