Chemistry2050 IntroductiontoOrganicChemistry FallSemester2011 Dr.RainerGlaser Examination #1 Practice Edition 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
Question 1. Atomic Structure and Lewis Structures. (20 points) (a) Carbon atom has 6 electrons. Provide the electron configurations of carbon 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) Explain briefly why carbon usually forms 4 bonds. (2 points) Promotion of one 2s electron to 2p z AO gives four unpaired electrons. (c) Draw complete Lewis structures of NO and NO -. 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 7 Cl. (e) Draw the three most important resonance forms of carbonate ion, CO 3 2-. Draw complete Lewis structures (all lone pairs, formal charges). Use the correct resonance arrow between the resonance forms. (6 points) 2
Question 2. Nomenclature of Alkanes, Alkenes & Alkynes. (20 points) (a) Draw the complete, unabbreviated structural formula of 2,2-dimethylpentane. (b) Draw the line-segment formula of 3-ethylcyclohexene. (c) Give the IUPAC name of the structure shown. 2,3-dichloropentane (d) Give the IUPAC name of the structure shown. 1,3-dimethylcyclohexane (e) Give the IUPAC name of the structure shown. 4-methylcyclohexene 3
Question 3. Conformations of Alkanes. (20 points) (a) Provide a perspective drawing of the eclipsed conformation of ethane. Perspective Drawing (b) Provide a Newman projection of the staggered conformation of ethane. Newman Projection (c) Provide a perspective drawing of the gauche conformation of butane. Perspective Drawing (d) Provide a Newman projection of the trans conformation of 1,2-dichloroethane. 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 the one on the right 4
Question 4. Reactions of Alkanes. (20 points) (a) Provide the stoichiometry of the complete combustion of ethane. (3 points) 1 H 3 C CH 3 + 3.5 O 2 2 CO 2 + 3 H 2 O (b) Provide the structures of the two products of monochlorination of 2-methylpropane. Circle the product that will be formed in larger amounts. (6 points) major, circle (c) Provide the structures and the IUPAC names of the two possible products of dichlorination of ethane. (No need to indicate conformation; we are only interested in connectivity.) 1,2-dichloroethane 1,1-dichloroethane (d) Provide the structure of the major product of monobromination of 2-methylpropane. (e) Provide the reaction equation of the initiation reaction of the radical chain chlorination of ethane. (3 points) Cl Cl (heat,light) 2Cl 5
Question 5. Reactions of Alkenes and Alkynes. (20 points) (a) For the electrophilic addition reaction of cyclopentene with hydrogeniodide (H I), draw linesegment structures of the substrate and the product. Provide the product s IUPAC name. (3 points) iodocyclopentane (b) Provide abbreviated structural drawings (show C C and C I bonds; do not show C H bonds, write CH, CH 2, CH 3 ) of the two products of the electrophilic addition reaction of 1-methylcyclopentene with hydrogeniodide (H I). Circle the Markovnikov product, i.e., the one formed in larger amounts. (4 p.) Markovnikov, circle this (c) The addition of 3 molecules of propene to borane, BH 3, forms tri-n-propylborane, B(CH 2 CH 2 CH 3 ) 3. This addition is remarkable in that the borane s H is added to the (more, less) substituted alkene carbon and, hence, the (Markovnikov, anti-markovnikov) product is favored. Workup with alkaline solution of H 2 O 2 (give reagent formula) affords (primary, secondary, tertiary) propanol. (d) Provide the structures of the two products of the ozonolysis of 1-butene (O 3 ; Zn, H + ). (4 p.) (e) Consider the HgSO 4 catalyzed hydration of propyne in mildly acidic media. This reaction initially forms an enol and the enol then rearranges to the final product. Draw the initially formed enol and draw the final product. This kind of rearrangement is a tautomerization because only the position of one H atom has changed. (5 points) 6