Columbia University C99ORG22ak.DOC Chem S3444Q Summer 99 Professor Irving J. Borowitz Exam No. 2 Answer Key July 28, 1999

Transcription

1 olumbia University 99RG22ak. hem SQ Summer 99 Professor Irving J. Borowitz Exam No. 2 Answer Key July 28, 1999 Name: Grade: Please use a non-red pen. Answer questions in the provided space. If you write any answers on the back of the page, indicate this on the front of that page. Points appear in parentheses ( ) and margin. Good Luck! Question Max. Pts. Pts Question Max. Pts Points = = = 22. ( + ) + ++ = 1. + ( ) + ( ) = = (1 ) Write a detailed mechanism for each of the following reactions. Use arrows to show electron flow. Total = 100 a. ( ) 2 = + 2 P dimethoxy ethane ( ) 2 = 2 + P= GRAERS: Accept loss of 0=P from either open dipolar or closed -membered ring forms b. Na, added slowl y 2 == = + 2 c. = + N 2 -N- + + fi =N-N + 2 Accept protonation either before or after carbonyl addition 1

2 2. (22) Fill in the missing reagents, or products A-I for the following reaction sequences. Sometimes more than one step is needed for individual conversions. a. l -= Li + -- Al(tBu) S 2 2 S/ + or 2 / Pd- poisoned catalyst or BF (Lindlar s catalyst) S S b N ANS= 1. Sl 2 or Pl 2. ( ) 2 uli or ( ) 2 d 6 c. --- d. ircle which molecule below reacts FASTER and give the product(s) of that reaction or N This ring is FASTER pt N, 2 e. Briefly explain the FASTER rate in 2d. The β-lactam (-membered cyclic amide) reacts FASTER since it has ring strain which is relieved upon opening pt 2 2 N 2 2

3 . (1) a. A compound, 10, reacts with 2,-dinitrophenylhydrazine solution to give a yellow precipitate. It gives a negative Iodoform test with I 2 / - and no reaction with cold KMn / -. The compound could be which of these. Answer= No. : -pentanone (1) () (2) () b. Write the IUPA name for each of the following compounds: (1) ( ) Br 2 trans or E--bromo-6,6-dimethyl--hepten-2-one (2) 2 2 N( ) 2 2 N,N-dimethylbutanamide ( ) 2 2 Ethyl 2-methoxy--pentynoate c. ircle the correct product formed from 2-methylpropanal dissolved in cold 2 / Na (trace). (1) () (2) 1,,2, 2pt Answer= No. d. Show the mechanism that produces this product. () 2 () () (6) 2 none of these 2

4 . (16) a. Rank the following compounds in order of decreasing acidity (strongest = 1 to weakest = ). 2 6pt (1) (2) () () () N 2 Ranking: 1 2 b. istinguish between the members of each of the following pairs of compounds by the requested number of chemical tests or reactions. Write the equations and the structures of all the major organic and inorganic products. Note the observations for the tests. ( 1 ) Use one test or reaction with equation and visible result and one specific IR or 1 - NMR fact to distinguish r : no color change r (or KMn, Tollens, etc.)) r + If a test: orange solution green r NaB : reduction to 2 alcohol reduction to a 1 o alcohol (very slow rxn with Znl 2 / l) (then a moderate rxn with Znl 2 /l R-l) IR = 1690 cm -1 R= 172 cm -1 Extra stretch ~2700 no quartet; δ 9. = (s,1); 7.1 (s,); 2 (t,2) NMR δ 1.2 (t,); 2. 2 (quart,2) : 2 mult 7-8 (ortho downfield) 2 = ( ca (sextet, 2) Not a singlet; no sextet ( 2 ) Use one test or reaction with equation and visible result and any two specific IR or 1 - NMR facts to distinguish l 6pt a, no reaction a. 2 : gives l b. Br 2 decolorizes if a test); if rxn: adds to double b. no color change (maybe slow reaction bond 2 (=)Br + Brl c. NaI/ Na gives I (yellow ppt) no yellow ppt ( rxn gives 2 2 Na) d. 2,-NP gives a yellow ppt R-( )=NN 6 (N 2 ) 2 no rxn e. R-N 2 : no rxn RN 2: converts the acid chloride to an amide 2 (=)NR f. Ag + no rxn Ag + gives Agl white ppt (rxn or test) IR: = 171 cm -1 ; no aromatic peaks = 1800; 2 peaks = ~ aromatic = 1600 NMR δ 2.1 (s,), vinyl s -6 no δ -6, no 2.1 but instead phenyl at 7.1 (s,)

5 (1) a. Write the structures of the reactant(s) that are used to make each of the following polymers: Note that more than one reactant may or may not be necessary. ( 1 ) N ( 2 ) N ( 2 ) n ( 2 ) 2 2 n b. Accurately name the above polymers. (1) Nylon-6 (-0. pt for Nylon-66) Pt (1. pt x 2) (2) poly (ethylene terphthalate); acron, polyester c. In the acid catalyzed hydrolysis of with 2 where is the isotopic label found in the products Explain by giving the mechanism and the products of the reaction. pt The 18 xygen is found in both the and the carbonyl group of the benzoic acid ( 2 ) product: c. Which of the following statement(s) concerning nitriles (R- N) is incorrect pt 1. nitriles can be hydrolyzed to carboxylic acids 2. nitriles can be formed from (many) alkyl halides by nucleophilic substitution by cyanide ion. nitriles can be reduced with excess LiAl to primary amines RN 2. nitriles react with RMgX (Grignard reagents) to form tertiary alcohols (incorrect ans.)**. nitriles can be made by dehydration of amides

6 a. a. 6. (19) o the following conversions. Fill in the missing inorganic/organic reagents, intermediates, and major products. Li 2 I b. S 2 l, 2 2 pt retention (cis) 2 pt inversion to trans Show stereochemistry at each stage c. NaB Et d. l 2 nly ketone is reduced (no stereochemistry implied) 2 pt should have a o amine (pyridine, Et N, etc) present to take up l ( ) 2 N e. ircle the compound below which is the strongest acid 2 pt 1. l l 2 l 2 2. l ll 2 *. 2 l 2 2 f. (2 pt) Explain your answer to 2e above using structures and words. 2,2-ichloroacetic acid is the strongest acid because of the two electronegative chlorines alpha to the carboxyl group: l l, 6

7 Scrap Paper July 28,