Chemistry 2050 Introduction to Organic Chemistry Fall Semester 2011 Dr. Rainer Glaser

Transcription

1 Chemistry2050 IntroductiontoOrganicChemistry FallSemester2011 Dr.RainerGlaser Examination #1 Bonding, Alkanes, Alkenes & Alkynes Wednesday, September 14, 2011, 10 10:50 am Answer Key Question 1. Atomic Structure & Lewis Structures 20 Question 2. Nomenclature of Alkanes, Alkenes & Alkynes 20 Question 3. Conformations of Alkanes 20 Question 4. Reactions of Alkanes 20 Question 5. Reactions of Alkenes & Alkynes 20 Total 100 1

2 Question 1. Atomic Structure and Lewis Structures. (20 points) (a) Nitrogen atom has 7 electrons. Provide the electron configurations of nitrogen in its ground state. Use the line format (one short line for each AO) to indicate the number of electrons in atomic orbitals 1s, 2s, 2p x, 2p y, and 2p z and indicate the spin (up or down) of the electrons. (2 points) (b) Provide the approximate value of the (H N H) angle in ammonia, NH 3, and state the hybridization at N in ammonia. (2 points) ca , sp 3 hybridization (c) Draw complete Lewis structures of NO (neutral) and NO + (cation). Draw all lone pair, show unpaired electrons and indicate formal charges. (6 points) NO NO + (d) Draw structural formulas for all possible isomers with the formula C 3 H 6 Cl 2. (4 points) An earlier version of the AK incorrectly showed ClCH 2-CH 2Cl-CH 3 (9/23/11). (e) Draw the three most important resonance forms of nitrate ion, NO - 3. Draw complete Lewis structures (all lone pairs, formal charges). Use the correct resonance arrow between the resonance forms. (6 points) 2

3 Question 2. Nomenclature of Alkanes, Alkenes & Alkynes. (20 points) (a) Draw the abbreviated structural formula of 2,2,3-trimethylbutane. Draw all C C bonds; you may abbreviate methyl groups as CH 3, a.s.o. (4 points) (b) Draw the line-segment formula of 5-fluorocyclo-1,3-hexadiene. (4 points) (c) Give the IUPAC name of the structure shown. Do not worry about configuration. (4 points) (trans- or E-) 2,3-dichloro-2-pentene (d) Give the IUPAC name of the structure shown. (4 points) cyclopentadiene, cyclo-1,3-pentadiene (e) Give the IUPAC name of the structure shown. (4 points) 1-pentyne, 1-pentine 3

4 Question 3. Conformations of Alkanes. (20 points) (a) Provide a perspective drawing of staggered conformation of ethane. (4 points) the Perspective Drawing (b) Provide a Newman projection of the staggered conformation of ethane. (4 points) Newman Projection (c) Provide a perspective drawing of the trans conformation of butane. (4 points) Perspective Drawing (d) Provide a Newman projection of the gauche conformation of 1,2-dichloroethane. (4 points) Newman Projection (e) Circle the more stable conformation of the molecule shown. The more stable structure adopts the chair_ conformation and the substituent prefers to be in the equatorial position. (4 points) Circle left 4

5 Question 4. Reactions of Alkanes. (20 points) (a) Provide the stoichiometry of the incomplete combustion of ethane to CO. (3 points) 2 H 3 C CH O 2 4 CO + 6 H 2 O (b) Provide the structures of the three products of monochlorination of 2,2-dimethylbutane. Circle the product that will be formed in the largest amount. (6 points) major, circle this (c) Provide the structures of the two possible products of tetrachlorination of ethane. (No need to indicate conformation; we are only interested in connectivity.) (4 points) (d) Provide the structure of the major product of monobromination of 2,3-dimethylbutane. (4 points) (e) Provide the reaction equation of the first propagation reaction of the radical chain chlorination of ethane (an H-abstraction). (3 points) H3C CH2 H+Cl H3C CH2 +H Cl 5

6 Question 5. Reactions of Alkenes and Alkynes. (20 points) (a) For the electrophilic addition reaction of cis-2-butene with hydrogenbromide (H Br), draw linesegment structures of the substrate and the product. Provide the product s IUPAC name. (3 points) 2-bromobutane (b) Provide abbreviated structural drawings (show C C and C Br bonds; do not show C H bonds, write CH, CH 2, CH 3 ) of the two products of the electrophilic addition reaction of 2-methyl-2-butene with H Br. Circle the Markovnikov product, i.e., the one formed in larger amounts. (4 p.) major (c) The Pt-catalyzed addition of hydrogen (H 2 ) to 1,2-dimethylcyclopentene forms 1,2-dimethylcyclopentane. This addition is remarkable in that the two methyl groups end up on (the same face, opposite faces) of the cyclopentane. This outcome occurs because the two H atoms are supplied from (the same face, opposite faces) of the cyclopentene in this (homogeneous, heterogeneous) hydrogenation reaction. (3 points) (d) Provide the structures of the two products of the ozonolysis of 2-pentene (O 3 ; Zn, H + ). (4 p.) (e) Consider the Diels-Alder reaction of butadiene and 1,1,2,2- tetracyanoethene. Draw the abbreviated structural formulas of both substrates and of the product; show C C and C CN bonds; do not show C H bonds; write C, CH, CH 2, CH 3, CN. (6 points) 6