Synthesis, Reactions, and Properties of Some Highly Hindered Diphenyl Ethers

Energy barriers to rotation about Ar-0 bonds have been obtained from an analysis of the variable temperature n.m.r. spectra of a number of highly substituted diphenyl ethers. These barriers are explained on the basis of structural and conformational effects and their implication for the resolution of optical isomers is discussed.Les barritres d'tnergie de rotation autour des liaisons Ar-0 ont ete obtenues i partir des spectres r.m.n. a temptrature variable d'un certain nombre de diphknyl ethers fortement substituts. Ces barrikres sont expliqutes en fonction des effets structuraux et conformationnels; leur constquence en vue de la rksolution d'isomeres optiques est discutte.

Section: Introductionmentioning

confidence: 99%

A Study of the Barriers to Rotation in Some Highly Substituted Diphenyl Ethers

Bergman¹,

Chandler²

1972

“…Allen and Moir (17) pointed out that eight such conformations exist for a diphenyl ether bearing four different ortho-substituents, and that these conformations can be divided into two classes of four each. The members of each class are interconvertible by synchronous rotations which do not require ortho-groups to be forced past each other, but a inember of one class can be converted to a member of the other only by surillounting this barrier.…”

Section: Fig 1 Asymmetric Diphenyl Ether Conformationmentioning

confidence: 99%

“…ZThe asymmetry of ethers of low steric hindrance has been shown by ultraviolet spectroscopy (1-3), dipole moments (4-7), electron and X-ray diffraction (8-lo), microwave absorption, and relaxation times (11)(12)(13)(14), and from theoretical calculations of ultraviolet spectra (15). For highly hindered diphenyl ethers, the fact has been assumed from a sttrdy of models (3, [16][17][18]. …”

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confidence: 99%

The Principal Conformations of Some Ortho-Substituted Diphenyl Ethers

Chandler¹,

Smith²,

Moir³

1964

Self Cite

A study of the nuclear magnetic resonance, infrared, and ultraviolet spectra showed that some doubly and triply ortho-substituted diphenyl ethers adopt, principally but not exclusively, the "H-inside" conformation, while the quadruply ortho-substituted 7-(4'-carbomethoxy-2',6'-dinitrophenoxy)metameconine (V) adopts the "methoxy-inside"conformation. Interconversion of conformational isomers is extremely fast. Reduction of methyl 4-methoxy-3-nitrobenzoate with tin and hydrochloric acid gave methyl 3-amino-2-chloro-4-methoxybenzoate.It has been well established2 that the principal conformations of diphenyl ethers, in solution or in the gas phase, are asymmetric ( Allen and Moir (17) pointed out that eight such conformations exist for a diphenyl ether bearing four different ortho-substituents, and that these conformations can be divided into two classes of four each. The members of each class are interconvertible by synchronous rotations which do not require ortho-groups to be forced past each other, Canada, Toronto, Jzcne 8 , 1963. ZThe asymmetry of ethers of low steric hindrance has been shown by ultraviolet spectroscopy (1-3), dipole moments (4-7), electron and X-ray diffraction (8-lo), microwave absorption, and relaxation times (11)(12)(13)(14), and from theoretical calculations of ultraviolet spectra (15). For highly hindered diphenyl ethers, the fact has been assumed from a sttrdy of models (3, [16][17][18]. 'Most of the material of this paper was presented at the national meeting of the Chemical Institute of3For convenience and clarity, a n unsltared pair is represented as essentially i n a p-orbital, the planes of the rings at right angles, and the C---C valence angle as near 90'. It will be u+tderstood that these are intended only as rough approxitnations suitable to the present qzcalitative discussion. Because the figure does not display the easy irtcrease in the oxygen valence angle, some of the conclusions of the paper seem more obvious, a priori, than i s justified.

“…( a ) A subject of continuing interest to us is the study of steric hindrance in dipllenyl ethers (3,6); obviously the ortho-chloro-and ortho-bro~no-phenols obtained in this work will alloxv the preparation of corresponding cliphenyl ethers with bloclcing groups of different sizes. (b) We hope to study the effect of crowding upon the quadrupole resonance frequency of the halogens; measurement of these frequencies is, of course, easier for chlorine compounds than for bromine or iodine compounds.…”

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confidence: 99%

“…The correct orientation of the co~npounds of the metameconine series (1,2,3,5,6) has rested upon the correct orientation of the derivatives of vanillin used a s reference compounds. I t seems proper to point out how heavily we have relied upon the careful worlc of Dr. Raiford6 and his students; of some 25 derivatives of vanillin needed in our structure proofs, only two (noted in the experimental part) have differed significantly from the descriptions given by these workers.…”

mentioning

confidence: 99%

Ortho-Substituted Chlorobenzenes Related to Metameconine

McRae¹,

Allen²,

Moir³

1961

Self Cite

Chlor~~iatcd derivatives of metameconine wcre formed for ihc first time. Partial demethylation of the derivatives with sulphuric acid occi~rred in highly selective fashion a t the 111ethoxyl ortho to the llalogen, without regard to the relative position of the carbonyl group which is Icno\vi~ to be highly directive for demethylatiolis in the absence of halogen. The phenolic products of the clemethylations are needed for the synthesis of sterically hindered cliphenyl ethers. They showed a type of intermolecular hydrogen bonding in the crystal which mas marlcedly subject to steric interference by thc halogen atoms.Our work with the cl~lorinated derivatives of metameconine (X) was first unc1c1-taken nlany years ago as a checlc upon the results we had obtained in the correspo~lding bromine series (1, 2, 3 ) ; these results had differed sharply fro111 those reported by others (4). The need for a check was emphasized when our inore recent worlc (5) led to solnewhat surprising conclusio~~s a s to the direction of brornination, nitration, and selective demethylation in the metameconi~les. This paper reports the independent characterization of the chlorine series of compounds, sllows that the chlorine series is an alnlost exact parallel to the bromine series, and therefore thoroughly verifies our previous results.TWO more reasons for proceeding with the chlorine series appeared later in our work.( a ) A subject of continuing interest to us is the study of steric hindrance in dipllenyl ethers (3, 6); obviously the ortho-chloro-and ortho-bro~no-phenols obtained in this work will alloxv the preparation of corresponding cliphenyl ethers with bloclcing groups of different sizes. (b) We hope to study the effect of crowding upon the quadrupole resonance frequency of the halogens; measurement of these frequencies is, of course, easier for chlorine compounds than for bromine or iodine compounds.The nlain novelty of the present worlc lies in the description of a n interesting steric. hindrance of hydrogen bonding in the solid phase. Synthesis a d S t r~l c t~l r eThe most easily available of the chlorine derivatives was 7-chloron~ctameconi~~c~ (XI I ) , made from metameconine (X) by nitration, reduction to the amine (XI) (1, 2, 4), diazotization of the amine, and the Sandrneyer reaction. No doubt the structure was obvious, since 7-bromomcta~~~econinc (1, 2, 4) and 7-iodometameco~li~le (1, 3), formed in corresponding ways, have had their structures tl~orouglily verified. Nevertheless the present I\-orl; offered a quite independent proof that the new substance was indeed 7-chlorornetameconine, its indirect formation from 2-chloroveratric acicl (XIV), as show11 in the chart, leaving no room for doubt as to its structure.The iso~lleric 4-chlorometameco~~i~~e (VII) was formed by the action of for~nalclel~ydc ilpon 5-chloroveratric acid (VI) in acid solution. The structure of the resulting phthaliclc