Exam2+key - Name _ Che-misty); 2311 Spring. 2009 Exam 2-...

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Unformatted text preview: Name _ Che-misty); 2311 Spring. 2009 Exam 2- Cha ters 3 and 4 Part I. Circle the answer to each of the following questions. [20 points] (1) The following transformation can be classified as: Wt; [W A an elimination [b] a substitution 0 [c] a rearrangement (d) an addition .01 Cl CH30H20H + CH3CH20‘Na+ _>- + Na+ Br + CH3CH20H -. I- -. -. '-- --.. Br [2] The following transformation can be classified as: (a) an elimination a substitution (c) a rearrangement [d] an addition CHIN“ “\“H CH3OH 'C—C“ OCH CH 0 Na+ ——-———> H’ \C/ 3 + 3 O H3COHIH..C Cn\\\\\H OH + N+CI' H/ a O (3] Which of the following molecules is the strongest acid? C—— C-—~—C (a) \ (b) \ I; OH q OH H 0 H300 (C) \C_ // \C_C// H’s \ chO/s \ (4) Which of the following represents the lowest energy conformation of 1,1- dichloro-2-methylpropane? I C! H A H30 H H C H H CI CI CI CH3 CH3 Cl A 3 H H CH3 (C) (d) H 01 Cl C' CH? CH3 (5) The following structures represent the various conformations of cis— and trans~ 4-tert-butyl-l-methylcyclohexane. Which is the most stable conformation of the cis isomer? CH3 H (a) (b) ' H H (Hsclsc CH3 rams C(CH3)3 t H krcm S H CH3 (C) CH3 H H (H3030 C(CHsls H ‘ Clé C15 if} (6] Which of the following statements is true? C [a] Ethylene (ethene) is a stronger Lowrey-Bronsted acid than acetylene (ethyne). b Acidity increases as pKa increases. Acidity of H-X increases as you go down a column on the periodic table. (d) Chloroacetic acid is a weaker acid than acetic acid. 8 [7] What is the general molecular formula for an acyclic alkene? A [8) What is the approximate dihedral angle between the two methyl substitutent in a chair conformation of trans—1,2—dimethylcyclohexane? ' 60° [b]109.5“ [c)120° (a) 180° C [9] The pKa for the ionization of acetic acid in water is 4.75. Which of the following values is the corresponding Ka? (a) 4.63 x 10'5 [b] 4.63 x 10‘4 @176 x 10-5 [d)1.76 x 10‘4 C [10] The C-C-C bond angles in c clohexane are approximately [a] 60° (b) 104.50 @1093) [d] none ofthese Part II. Designate True (T) or False [F] for each of the following statements. [20 points] F (1) Carbanions are electron deficient electrophilic species. T [2] The weaker the Lowry-Bronsted acid the stronger the conjugate base. ’T [3) A chloro substituent attached to a carbon exhibits an electron withdrawing inductive effect. F [4] Exothermic reactions have a positive [+] enthalpy of reaction. T [5) The temporary molecular shapes that results from rotation of groups about single bonds are called conformations ofa molecule. T [6] The barrier to rotation about a single bond is called the torsional barrier of that particular single bond. F (7] The diaxial conformation of cis-1,3—dimethylcyclohexane is more stable than the diequatorial conformer. T (8) The cis isomer of 1,2—dimethylcyclohexane has one methyl group axial and the other methyl group equatorial. T [9] A hydrogen attached to an sp carbon is more acidic than a hydrogen attached to an sp2 carbon. T (10) A negative value of AG" is associated with reactions that favor the formation of products when equilibrium is reached. Part III. Nomenclature. [28 points) (1) Write bond-line structures for each of the following compounds: 1{ M [a] vinylcyclopropane (b) cyclopropylcyclopentane [c] neopentylcycloheptane [d] 2,2-dich]oro-3-methylpentanol (2] Give systematic IUPAC names for each of the following compounds: (a) CH /%°H A/‘CH’J /”3'ISOFO I’bl'hlLad‘ml (b) 0 55 -c clooo‘ucllene. OH (c) HO H H H - H H H 0‘5 " 67:0, - [DJ/)CXCILIIO' [b] 25°, '1 atm. Part V. Confomational Analysis. (20 points) M [a] Using Newman projections, draw and label all staggered and eclipsed (4' conformations that result from rotation around the indicated bond. Identify the K lowest and highest energy conformations. o o a 0 v5 (0/390) (60) (110 D H CH3 H \ Cl A H H H\\\“" ""“IH H H H H a H H Cl H m ._ {ML (LON 5W («two a) o 0 u .2 00+ I 5/5; mead HQ“; (‘5‘ CH3 £240) (300) Jr“ WWW A H H Cl H H I? . H H HH achesul (b) Draw a diagram showing potential energy vs. torsional angle for the Newman projection representations above. c Cl h M >~ (eggsecr can» \D 9; Ln 2 w _.| S F. 2 {.2 0‘3 (ma _ lowest energy) 0 to :20 I80 240 300 39:0 1395wa ANGLE C) fir “LL (/afieli'HEI-w ...
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This note was uploaded on 02/22/2012 for the course CHBE 2300 taught by Professor Kawajiri during the Spring '08 term at Georgia Tech.

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Exam2+key - Name _ Che-misty); 2311 Spring. 2009 Exam 2-...

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