practice midterm solutions

practice midterm solutions - SJ*ur'*" CHM3 lZZ _p...

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SJ*ur'*" CHM 3lZZ _ practice exam 2010 I Note thatthis sample is longerthan the midterm ofOctober 20 will bel l. Short answers : (a) Determine the degree of unsaturation of a compound with molecular formula CrH3ClrOr. 2rl - L(s+ 3) -- o {b) Protons have a Larmor ffequency of4O0 MHz in a magnetic field of 9.4 T. What the !armor frequency of protons in a magneticfield of 18.8 T? n'VBo Z1? tg-tr T- f)oAHz (c) Why is proton (rH) NMR more sensitive (better sign a fto_noise) th a n 13C NMR ? ,44 e'A-'n J qbq^/a. .t /Loar.4/ttj1n-,- razl'o (d) Does a cross peak in a NOESy spectrum indicate thatthere is a./coupling between the two protons which are correlated? Expla;n. 4./ ) . ,,v Dc JJ j , , ,, tlr^1/ - yu '- ,ar;*,*_,fics. (e) lf you want to improve the signa!to,noise ratjo ofyour 13c NMR spectrum, jt befter to (i) double the concentration ofthe sample or (ii) record twice the nurnber of FID scans? fL'! .ct4cz4 L.-y',*.t
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(f) Explain why the intensities ofthe peaks in a triplet due to coupling of a proton with two equivalent spin-1/2 nu.leidiffer from those ofthe triplet resu ting
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practice midterm solutions - SJ*ur'*" CHM3 lZZ _p...

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