CHM 233 : Fall 2018 Quiz #9 - Answer Key

Transcription

1 HM 233 : Fall 2018 Quiz #9 - Answer Key Question 1 M25c How many different signals would you expect to see in a proton-decoupled carbon nmr spectrum of the following compound? A 3 B 4 6 D carbons circled with the same color are magnetically equivalent

2 Question 2 M25j Which correctly describes the number of signals seen in the proton decoupled carbon nmr spectra of the following 3 compounds (i, ii and iii)? l i ii H 2 iii 2 H A 7 signals for i, 5 signals for ii and 6 signals for iii. B 11 signals for i, 10 signals for ii and 8 signals for iii. 7 signals for i, 4 signals for ii and 5 signals for iii. D 8 signals for i, 4 signals for ii and 7 signals for iii H 2 l H

3 Question 3 Mnmr2 Identify the most deshielded carbon atom in the following structure as that labelled A, B, or D. B D A N H2 atoms are deshielded by proximity to electronegative elements and unsaturation (double bonds) B D A N H2 arbon A is part of a double bond and is adjacent to the electronegative nitroge, it is the MST deshielded arbon B is not part of a double bond, is adjacent to the electronegative nitrogen and the unsaturation, it is the second most deshielded arbon D is not part of a double bond, it is adjacent to the unsaturation but is remote from the nitrogen, it is the next most deshielded arbon is remote from both the unsaturation and the nitrogen, it is the LEAST deshielded.

4 Question 4 M25n Which compound has the following nmr spectrum? 3H singlet 6H doublet 1H 1H triplet doublet 1H 1H doublet triplet 1H septet H H H H A B D

5 Question 5 Mnmr4 Which carbon would be the LEAST deshielded in methyl pyruvate? B A methyl pyruvate atoms are deshielded by proximity to electronegative elements and unsaturation (double bonds). part of = bond, very deshielded A D part of = bond, very deshielded adjacent to electronegative oxygen, fairly deshielede although the atom of the = bond has a partial positive charge due to dipole moment associated with the = bond, carbon A is not as deshielded as carbon D, opposite D

6 Question 6 M25m How many different signals would you expect to see in a proton-decoupled carbon nmr spectrum of the following compound? H A 7 B 8 9 D 10 1H in this case none of the carbons in the ring are magnetically equivalent, the only magnetically equivalent carbons are the 2 -Me of the isopropyl group 6 is NT equivalent to 3 because 3 is closer to the -H substituent and 6 is closer to the i-pr substituent 5 is NT equivalent to 4 because 5 is opposite to the -H substituent and 4 is opposite to the i-pr substituent

7 Question 7 Mnmr1 How many different signals would you expect to see for in both a proton and also a proton decoupled 13 NMR spectrum of the following molecule? H 2 H 2 A 6 in the proton spectrum and 7 in the 13 spectrum B 4 in the proton spectrum and 5 in the 13 spectrum 3 in the proton spectrum and 4 in the 13 spectrum D 3 in the proton spectrum and 3 in the 13 spectrum 3 kinds of magnetically inequivalent hydrogens H 2 H 2 magnetically equivalent hydrogen atoms are indicated by color code 4 kinds of magnetically inequivalent carbons H 2 H 2 magnetically equivalent carbon atoms are indicated by color code, don't forget this one

8 Question 8 Mnmr5 How many signals would you expect to see in the protondecoupled carbon nmr spectrum of the following molecule? A 6 signals B 7 signals 8 signals D 9 signals atoms with the same color symbol are magnetically equivalent, and contribute to the SAME signal