Question

Practice Problems: 1a. Analyze the given H NMR spectrum of 3-methyl-2-butanone. Explain why there are 3 different signals. Assign the signals to the correct H's. 3-methyl-2-butanone 1b. Do the observed splitting patterns follow the N+1 rule? Explain. .2 3.0 2.8 fi (ppm) 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0. Be very careful: it is NOT the number of H's giving rise to a signal that determines its splitting pattern. Instead, it is the number of H's bonded to the adjacent carbon atoms that determines the splitting pattern. Page 107

Answer 1

Ans 1 Cal cin -rom llal - CH. HC H 2 we get signals in thNmR due to magnetic field generated by adjacent Carbon atom's prodons. or we can say the speceis which is different chemical environment give different signals in AH NMR. such as proton CH₂ = Give a strong Singlet due to schree protons of methyl group It is singlet because there is no proton on adjacent carbon. s chemical schieft) = 2.92 bbm 2 for proton Ho= Septed due to sixe protons on adjacent or vicinal carbons. cs.canned with CamScanner

S = 2.3-2.8 ppm (from spectra) For proton (c) = A strong doublet due to single proton tb. S = lor 1.2 ppm carton - There are three different signals because of difference in cchemical environment. such as proton (a) of methyl group tare attached - e-group. Proton Ho - are on carbon which is bonded to & group as well as with two methyl group. proton Hc. on two methyl group are present on carbons which is adjacent to a carbon which chas only 1 proton. An. 1 (6) Yes got follow N+1 rule. N+ 1 rule- means a proton signal o split into N+1 beaks due to coupling 'cs.canned with CamScanner

witch protons on vicinal cas bons. where N = Number of protons vicinal carbons. on Ex- for proton Ha= Signal is singlet because here N= o so N+1 = 1 For proton Ho = septet due to N=6 N+1 = 6+1 =7 for He= Doublet because N=1 Nt1 = tl - 2 CScanned with CamScanner