t [Reprinted from the Journel of thc Ameri.a!

I

1

I'

Cheqicd

Society, t?, 1058 (1965).1

Nucl ear MagneticResonanceSpectroscopy. The Effect of Solvent on Magnetic Arising from Nonequivalence MolecularAsymmetry

GeorgeM. Whitesides,John J. Grocki, David Holtz, Herbert Steinberg, and John D. Roberts

' copyright

chemical society, S?, 1058 (196'i)'l [ILelrrinted from the Journal of the American by permission of tbe copyright owner' reprinted and society chernical the Americau 1965 by

Nuclear Magnetic ResonanceSpectroscopy' The Effect of Solvent on Magnetic Nonequivalence Arising from Molecular Asymmetry'" G e o rg eN I. Whi tesi des,John J. Grocki , D avi d H ol tz' and John D . R oberts H e rb e rt Ste i nberg,tb of chemisl,'l:' Contribttriortl,{o. 3.l57from rhe Gates and crellin Laboratorics culiforniu. Pasadenu. Technolog)" california Instiruteof R e c e i v e dS e ptember18, 1961

Thc clrcntical shiJ'r betv,een the gemirnl methy'lcnc prototrs of l-phent,lethl'l bcnzt,lcther has beenmeasurecl 'itt 4 variet1, of solvents. ,4n trpproximute correlatiorr obsert,eclbetyrean .solvenl dielectic cottsluilt and rhe c legr eeof t he m u g n e ti cn o n e q ri v a l e n coaf the rnethyl ctta v 3. is discussedin light of similar results protons, v.1 suggestedthat for structurrtll.l,reluted contpounds. It is changes refect maV tttith solvent v6 vA irr the variation itt the conformotion of the henzt'lic phenvl ring w'itlt respectto the meth.t'lenegrouP. Introduction I n a pr ev io r' rsp a p c r.r c o rre l a ti o n s h a l' e been dev eloped bet w e e n th e d e g re e o f th e magneti c nonequiv alenc eof th e p ro to n s o f a m e th y l e n egl oup cl ose t O an ls y m nletri c c e n te r3a trc ith e s tru c tu reo [ the nr.ol e( l ) ( a ) S u p p o r t c c li n p i t r t b y t h e O f t i c e o i ' N a v a l R e s c u r c ha n d t h c Scielce u ' t l e r g r a c l t r a r cr e s c u r c hp a r t i c i p a t i o r tp r o g r i l l l ro f t h c N a t i o r r a l , 963' F o u n d a t i o n ; ( b ) N ' A . T . O ' F e t l o r v1 ( 2 ) G M . W i r i t c s i c l e sD, . H o l t z . n n < jJ ' D ' R o b c r t s 'J " ' l n r ' C h e t n ' -S o c . , 8 6 , 1 6 2 8 ( 1 9 6 ' t ) . ( 3 j 1 . n et e r m " a s y i n m c t r i cc c n r e r "u s e di ^ t h i s p a p c rr e f e r st o t h e s i n g l e r v h i c l rb e a r s f o u r c a r b o n a t o m i i r e i r c h o f t h c c o l n p o u t r d se x a m i n e d of stcreod i l l ' e r e n tS u b s l i t u c p t s . A s i m i l a r m a g n e t i c r l o u e q u i v a l e n c c also been c h e m i c a l l _d" -i s r i n c t g e m i n a l m e t h y l e n ep r o t o t l s h a s o f ' c o u r s c clissymmetriccompottpds [c/'. W' L' fvfeyer observe ll E I ql Ll

Ethyi

in solute' The experi" Solutionsrvere l0 + 2% by volume 0'5 c'p's' 6 From than greater no is vB v^ in error mental ref. 2.

ta r\ v

Solvent

^ l

.=l ()l

=l

rll

;1 l' l

r)

?l ol

-l ;l

ra

.'l

V

V

VV

O I

I

ai

an

I

-l lrl

Tab|elV.ChemicalShift(c.p.s.)betrveentheMethyleneProlons of Solvent' of t-ef,.nylethyl Neopentyl Ether as a Function v.r - t/B Solvent ,/B Y.q, Solvent Benzene Toluene Cyclohexane n-Pentane Bromobenzene Carbon disultide

I

Nl

tl a-t

a-l

aa

I

! l q l - l

(.

ca

VVV

VV

I :-

ri

30