Chemistry 2030 Survey of Organic Chemistry Fall Semester 2017 Dr. Rainer Glaser

Transcription

1 Chemistry 2030 Survey of Organic Chemistry Fall Semester 2017 Dr. Rainer Glaser Examination #1 Bonding, Alkanes, Alkenes & Alkynes Thursday, September 14, 2017, 8:25 9:15 am Name: Answer Key Question 1. Atomic Structure, Lewis Structures, and Hybridization 20 Question 2. Nomenclature of Alkanes, Alkenes & Alkynes 20 Question 3. Conformations of Alkanes and Cycloalkanes 20 Question 4. Combustion Reactions of Hydrocarbons 20 Question 5. Halogenation Reactions of Alkanes 20 Total 100 ALLOWED: Periodic System of the Elements (printed, w/o handwriting on it). Molecular models (you can bring pre-made models). Simple, non-programmable calculator (not really needed). NOT ALLOWED: Books. Notes. Electronic devices of any kind (other than a simple calculator). 1

2 Question 1. Atomic Structure and Lewis Structures. (20 points) (a) Neutral 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. (3 points) (b) Neutral phosphorous atom has _15_ electrons. Provide the electron configurations of phosphorous in its ground state using the line format as in part (a). (3 points) (c) Draw the requested structures of chloroethane. You may use abbreviated structural formulas but show all C C and all C Cl bonds. (8 points) Complete Lewis Dot Structure Complete Lewis-Kekule Structure Perspective Drawing (wedges) Line Segment Drawing (d) Draw complete Lewis structures of NO 2 + (cation) and NO 2 (neutral). Draw all lone pairs, show unpaired electrons (if any) and indicate formal charges. One Lewis structure suffices for NO 2 +. For neutral NO 2, draw several resonance forms using resonance arrows and the correct brackets. (6 pts.) NO 2 + NO 2 2

3 Question 2. Nomenclature of Alkanes, Alkenes & Alkynes. (20 points) (a) Draw the abbreviated structural formula of 2- bromo-2-chloropentane. Draw all C C, C Cl and C Br bonds; you may abbreviate methyl groups as CH 3, methylene groups as CH 2, and so on. (4 points) (b) Draw the line-segment formulas of 1,3-cyclohexadiene and of 1,4-cyclohexadiene. For each compound, write in the box whether the double bonds are cumulated, conjugated or isolated. (6 pts.) 1,3-cyclohexadiene 1,4-cyclohexadiene conjugated isolated (c) Give the IUPAC names of the isomeric structures shown. (6 points) Name of structure on left: Isopropylcyclohexane Name of structure on right: Propylcyclohexane (d) Give the IUPAC name of the structure shown. (4 points) Name: 3-Octyne, Oct-3-yne 3

4 Question 3. Conformations of Alkanes. (20 points) (a) Draw Newman projections of staggered (left) and eclipsed (right) ethane. (4 p.) (b) Four models are shown of 1,2-dichloroethane. For each model, state whether the conformation about the central bond is staggered or eclipsed. For each model, state the name of the conformation (i.e., trans, cis, gauche); if the conformation does not have a name, write no common name. (8 points) Eclipsed no common name Staggered gauche Staggered trans Eclipsed cis (c) Structures are shown of chlorocyclohexane. For each structure, write next to it whether it is in a chair or a boat conformation. For each structure, write next to every chlorine atom whether it is in an axial (ax) or equatorial (eq) position. Circle the most stable structure. (8 points) boat, equatorial boat, axial chair, equatorial chair, axial 4

5 Question 4. Combustion Reactions of Hydrocarbons. (20 points) (a) Provide the stoichiometry of the complete combustion of hexane to CO 2. (3 points) 2 C 6 H O 2 12 CO H 2 O (b) Provide the stoichiometry of the incomplete combustion of cyclohexane to carbon (soot). Begin by indicating the number of H atoms in the sum formula of cyclohexane. (4 points) C 6 H O 2 6 C + 6 H 2 O (c) Lewis-Kekule structures of O 2. Draw the structure for the closed shell molecule on the left; this structure has no unpaired electrons and both O-atoms have an electron (sextet, heptet, octet). Draw the structure of the molecule in its ground state on the right; this structure has 2_ unpaired electrons and both O-atoms have an electron (sextet, heptet, octet). The ground state of O 2 is a (singlet, doublet, triplet, quartet), that is, the unpaired electrons have (parallel, anti-parallel) spins. (7 points) (d) The first step of the combustion of ethane consists in the abstraction of one H atom by O 2. Draw the complete structures of C 2 H 6, O 2 and of the reaction products of this first step. This reaction is a (homolysis, heterolysis). Indicate the electron flow using the correct curved arrows. (6 points) 5

6 Question 5. Halogenation Reactions of Alkanes. (20 points) 2-methylpropane: H 3 C CH(CH 3 ) CH 3 (a) Draw structural formulas for all possible isomers formed by monochlorination of 2-methylpropane. You may use abbreviated structural formulas but show all C C and C Cl bonds. Circle the product that will be formed in the largest amount. Give the percentage yield you expect for the major product. (8 points) 90% : 10% (b) Draw structural formulas for all possible isomers formed by monobromination of 2-methylpropane. You may use abbreviated structural formulas but show all C C and C Br bonds. Circle the product that will be formed in the largest amount. (6 points) (c) Draw structural formulas for all possible isomers formed by dichlorination of 2-methylpropane. You may use abbreviated structural formulas but show all C C and C Cl bonds. Circle the product that will be formed in the largest amount. (6 points) 6