Name: ________________________________________ Chem 204 Spring 1985 Exam II: Chaps. 7(except 7.7), 8(except 8.4, 8.5) 9, 10.1‐10.6, 10.9, 10.12, 14.8A and Lecture Bklts. Partial credit will be given when/where appropriate. Brief answers are most welcome, citing specific experimental support from text or below. Long, rambling answers are not necessary! Note: There is no particular order to questions presented here. Answer first those questions you know best. Partial credit will be given when/where appropriate. Brief answers are most welcome, citing specific experimental support from text or below. Long, rambling answers are not necessary! Useful Information: pKa of Acids pKa's of Acids: at 25°: ΔG° = ‐2.303 RT log K = ‐1.366 log K (kcals/mole) H2SO4 ‐12 CH3SO3‐H <0 RNH3+ 10 HI ‐9 H3PO4 2.2 CH2(CN)2 11.2 HBr ‐8 HF 3.2 H2O 15.7 HCl ‐7 CH2(NO2)2 3.6 Alcohols 16‐19 +
H3O ‐1.7 H2S 7.0 (CH3)CO 20 HCN 9.1 H‐N+≡N <0 R‐C≡CH 25 +
+
H‐O R2 <0 NH4 9.2
CH3CN 25
+
H‐S R2 <0 C6H5OH 9.9 NH3 to R2NH 35‐36 alkanes RH 40‐60 O
O
O
O
CH3
C
C
C
C
25 4.8
11 CH3
CH2
O
CH3
O
CH3
OH
CH3
Supplies: Common Solvents of all kinds: non‐polar; hydroxylic; dipolar, aprotic Inorganic Reagents, including SOCl2, CO2, Mg, Na, K, Li, Al, NaN3, PX3, CrO3, ZnCl2, D2O, AgBr, AgNO3, RCN, NaSH, NaOH, NH3, H2SO4, HX (Cl, Br, I), NaSCN, NaH, KSCN, KCN, NaSH, NaOH, NH3, H2SO4, HX(Cl,Br,or I), NH2OSO3H, I2, Ag2O, Zn(Ag), Zn(Cu), LiX (Cl, Br, I), NaI, NH2OH, NH2‐NH2, Raney Ni, Hg+2, CrO3, KMnO4, H2O2, OsO4, B2H6, ZnCl2 Non‐cyclic Organics: one thru five carbon alcohols, H‐C≡C‐H, CH3CO2H, , CH3SO2Cl, CH2=O, (C2H5)3N, (CH3)2SO4, "PCC", CH2=CH‐CH2‐OH, acids, aldehydes, amines, alkenes, alkynes, ketones, thiols (R‐SH); H‐C≡C‐H, CHCl3, CCl4, CH2=CH‐CH2OH, CH2I2, (C2H5)3B, NO, HO‐CH2CH2OH, HS‐CH2CH2SH, (CH3)3SiCl, CHBr3, CBr4 CF3CO3H (pertrifluoroacetic acid), CF3‐SO2Cl (for "triflates"), CH2=CH‐Br, CH2N2, CH2=C=O Cyclic Organics: Cyclopropanol to Cycloheptanol, C6H5‐SO2Cl, pyridine, p‐CH3C6H4SO2Cl or O
CH3
S
Cl
CH2
OH
O
(for "tosylate" prep.), , CH2 CH2 ,Cyclopropanol to Cycloheptanol, C6H5SO2Cl, pyridine, C6H5‐CH2‐OH, C6H5‐NH‐NH2, m‐ClC6H4CO3H ( a per‐acid), C6H5‐CH2‐Br, C6H5‐CO2H, C6H5‐CH3, C6H5‐C(O)‐O‐O‐C(O)‐C6H5 (a peroxide), m‐ClC6H4CO3H ( a per‐acid),PPh3 Bases (Strong); Reducing Agents: NaH, KH, LiN(‐iPr)2 ("LDA"), LiAlH4, NaBH4, CH3Li, KN(SiMe3)2, C6H5‐, LiAlH(O‐t‐Bu)3 O
1. (22) O
+ HBr
C5H9BrO + H2O
CH3
CH2OH
When I (Aldrich: $9.50/10g) was heated with HBr (consider reaction only at alcohol), it yielded only a rearranged substitution product, C5H9BrO. a) Using the mechanism knowledge gained from Chapters 9 & 10, draw a mechanism (more than one step) for this reaction, and thereby predict the "most reasonable" structure of C5H9BrO. (Do some "Scratching" on the page opposite first.) Label the "slow step". b) What are the two driving forces behind this rearrangement? c) Outline the best possible series of reactions to connect (I) into the unrearranged substitution product, (II). O
CH3
O
CH2OH
CH3
CH2Br
H
O
2. (12) (III) is a component of the sex pheremone of the male ghost moth ‐‐‐ usually female moths do the attracting! (Tet. 563 (1985)). Letts., a)
(III)
O
Give the "priority" of substituent’s at the chiral center of (III), the most important being listed first: b) What is the R/S designation at this center? c) Based on ring atom hybridization (cite some), what do you expect is the general shape of the ring portion of (III)? Discuss briefly. d) Were (III) to be added to CH3CH2‐MgBr/ether and the reaction later hydrolyzed (H30+), what would form? 3. (11) a) Draw the unique configuration of (S)‐(+)‐1‐bromo‐2‐methylbutane (Aldrich: $7.90/g). b) Allowing (II), the bromide in (a), and the two bromides shown below to each react with NaN3‐ in solvent ethanol (same temp.), what is the relative reactivity order to be expected insofar as substitution is concerned? Rank in decreasing order: i.e. label as (1) being the fastest, etc. What is the fundamental factor that determines this rate order amongst the 4 compounds? Br
Br
4. (24) Consider the following reaction of (IV): CH3
H
C
OCH3
+
+ NaOCH3
H
C
+
Br
CH3
(IV)
(V): Diether
a) Draw the three products formed, indicating their unique configuration where needed. (Hint: What “kind" of a nucleophile present?) b) Will product V be optically active? __________________. Give the basis of your answer, briefly. c) (Choose one:) 1) If (V) is optically active, draw a stereoisomer of (V) that is optically inactive, if such exists: 2) If (V) is optically inactive, draw a stereoisomer of (V) that is optically active, if such exists: d) (V) and the stereoisomer drawn in (c) are related as a pair of _________________ (term). e) Carefully sketch the transition state leading to the formation of one of the products in the above reaction other than (V). 5. (12) a) 0.3 M C2H5MgBr/ether (Et‐O‐Et) is actually a complex equilibrium mixture of what species? Include what state they actually exist in the ether solution, when drawing structures. C
O
b) Essentially the same sort of reaction outcome that C2H5MgBr gives with (carbonyl) can be obtained with what other organometallic? Show its preparation. CH3
6. (10) a) Designate the chiral center(s) with the appropriate R/S indications; Cl
include priority in your answer. b) (III) (0.025g), when dissolved in 10 ml water and placed in a 5 cm‐long polarimeter tube, gives a = +0.20°. Calculate the specific rotation of (III). O
7. (20) When a mixture of isopropyl alcohol in dilute H2SO4 is heated to 100°, essentially no significant, reaction occurs! However, if you add, dropwise, an equivalent amount of tert‐butyl alcohol to the above mixture, rapid reaction occurs to give CH3
CH3
CH3
O
C
CH
CH3
CH3
(VI)
Potential Energy
a) Draw a mechanism accounting for the formation of VI. Label the slow step. b) Briefly, why does the reaction take place once tert‐butyl alcohol is added? Explain in terms of possible reaction intermediates. c) Sketch a reaction progress diagram for the mechanism in (a), making sure the # of hills equals the # of steps. Generally speaking, H+‐ transfers involving oxygen’s have low Eact. Label the overall Eact, and indicate what the valleys "contain". Reaction Progress
8. (24) a) Given VII ($13.50/10g), outline a series of chemical reactions (minimum #, consistent with good yield) to transform it into VIII. THINK BACKWARDS/retrospectively! All other supplies: see cover and/or prepare them. Br
(VII)
OH
(VIII)
b) Continuing, how would you prepare (IX) from (VIII)? Again, think retrospectively. OH
(VIII)
C
CH
(IX) c) Rank the leaving group abilities of the following (i.e., #1, the best, etc.): R‐SH, R‐N2+, R‐F. Point out the basis for your decision. d) What would be the single molecule you would treat with dilute NaOH to allow formation of (X)? S
NaOH
(X)