Final - Fall 2006

Final - Fall 2006 - Final Exam F2006: Comments 1. (4 pts)...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Final Exam F2006: Comments 1. (4 pts) Arrange the following phenols in order of increasing acidity (least to most acidic). OH OH OH OH NH 2 NO 2 A BC D F CN a) A < B < C < D b) D < C < A < B c) C < D < B < A d) C < D < A < B e) D < C < B < A Comments: This question tests the understanding of EDG/EWG effects and the ability to write resonance forms. It is essentially identical to 4TS: 68, and correspond to book material on p. 594-595. 2. (4 pts) Which of the following species are aromatic? N N H N I II III IV V a) I and II b) II and V c) IV and V d) I , II , and III e) II , III , and V Comments: This question tests the concept of aromaticity. There are multiple questions of that nature throughout the practice exams and training sets (for example: TS4: 45, PE4A; 19, PE4C: 25,). The only thing required is to recognize which systems have the complete ring of π orbitals and (4n+2) π electrons.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 3. (4 pts) In the reaction shown below, the carbon marked by a dot (•) is 13 C isotope that can be distinguished from “normal” carbons ( 12 C) by a special kind of spectroscopy. H 2 SO 4 Which structure shows the correct position of 13 C in the product of the carbocation rearrangement shown above? a) b) c) d) e) Comments: This question is an example of a carbocation rearrangement. An almost identical case was discussed in detail in class (check October 20 News), and numerous similar examples were in practice set (see for example TS4: 28, PE4B: 4, Book: 6.49). A simple pencil-and-eraser technique is enough to answer this question. 4. (4 pts) What is the crucial intermediate with the correct mechanistic arrows for the ring-opening reaction of the epoxide shown below? O ? 2. H 3 O + Product 1. CH 3 MgBr O H + O O O a) b) c) d) H 3 CM g B r H 3 gB r H 3 r H 3 r Comments: This is an example of nucleophilic ring opening of epoxides. It was sufficient to recognize that this is an S N 2 reaction, with the release of ring strain, providing the driving force. S N 2 reactions take place on the back-side of the leaving group ( σ * C-O bond is the LUMO) and on the less sterically crowded carbon. Grignards as strong bases cannot coexist with acids (excluding (a) as an option). Similar example was in TS4: 74.
Background image of page 2
3 5. (4 pts) Which of the following statements about A and B is true? AB a) They are different conformations of the same molecule. b) They are constitutional isomers. c) They are diastereomers. d) They are enantiomers. e) They are identical. Comments: The question was designed to test your understanding of stereochemical representations. It cannot get any simpler: just rotate B by 180 o to see it. There was no direct precedent for this question, but it tests a very basic concept, and there were questions about interpretation of stereochemical drawings on previous exams. 6-7 . A Chem-38 student had only the following reagents available to accomplish the transformation given below: a) KMnO 4 /H + f) BH 3 ; H 2 O 2 / HO b) H 2 /Pd/C g) NBS/DMSO/H 2 O c) OsO 4 ; NaHSO 3 h ) H 2 /Lindlar’s catalyst d) Li/NH 3 (liquid) i) HIO 4 e) Hg(OAc) 2 /H 2 O; NaBH 4 j ) H 2 SO 4 /SO 3 6. (4 pts) What reagent was employed to carry out the third ( III ) step?
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 12

Final - Fall 2006 - Final Exam F2006: Comments 1. (4 pts)...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online