8. In NMR terminology, protons H, and H, are said to be a. identical b. enantiot

Question

8. In NMR terminology, protons H, and H, are said to be a. identical b. enantiotopic c. diastereotopic d. homotopic e. mesotopic structure shown, H, and H, are classified as: a. homotopie protons. b. vicinal protons. c. enantiotopic protons. d. diastereotopic protons. e. isomeric protons. 10. A bromodichlorobenzene which gives four signals in the broadband proton-decoupled 13c spectrum could be: a. 2-Bromo-1,3-dichlorobenzene b. 2-Bromo-1,4-dichlorobenzene c. 3-Bromo-1,2-dichlorobenzene d. 4-Bromo-1,2-dichlorobenzene e. 4-Bromo-1,3-dichlorobenzene 11. Which of the following dienes would you expect to be the most stable? a. CH3 CH CHCH-CHCH d. CH2 CHCHCH CH2 CH

Explanation / Answer

In proton NMR, the topicity of a proton is defined by the kind of stereoisomer that is obtained when one of the protons in scrutiny is replaced by another group or atom. Thus in question 8 it can be noticed that replacing either of the protons labelled a or b will result in the formation of diastereomers as the adjacent carbon is chiral and so these two protons are diastereotopic. In question 9 also, replacing either of the two protons results in different isomers which are not mirror images of each other but stereoisomers thus being diastereomers resulting in these two protons also being diastereotopic.

So, for question 8 the answer is OPTION C and for question 9 it is OPTION D.

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