Chemistry 2030 Survey of Organic Chemistry Fall Semester 2015 Dr. Rainer Glaser

Transcription

1 Chemistry 2030 Survey of Organic Chemistry Fall Semester 2015 Dr. Rainer Glaser Examination #1 Bonding, Alkanes, Alkenes & Alkynes Thursday, September 17, 2015, 8:25 9:15 am 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) Fluorine atom has 9 electrons. Provide the electron configurations of fluorine 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) Chlorine atom has 17 electrons. Provide the electron configurations of chlorine 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, 2p z, 3s, 3p x, 3p y, and 3p z and indicate the spin (up or down) of the electrons. (3 points) (c) Provide the values of the bond angles in methane and water. (H C H) bond angle in methane, CH 4 (H O H) angle in water, H 2 O (d) Which statement corretly describes the (H N H) bond angle in ammonia, NH 3? (2 points) Option 1: (H C H) < (H N H) < (H O H) Option 2: (H C H) > (H N H) > (H O H) Option 3: (H C H) < (H N H) > (H O H) Option 4: (H C H) > (H N H) < (H O H) (e) Draw the three most important resonance forms of nitrate ion, NO 3 -. Draw complete Lewis-Kekule structures (all lone pairs, formal charges). Use the correct resonance arrow and the correct brackets. (8 points) 2

3 Question 2. Nomenclature of Alkanes, Alkenes & Alkynes. (20 points) (a) Draw the abbreviated structural formula of 2- bromo-2,3-dimethylbutane. Draw all C C 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 formula of 1,4-cyclohexadiene. (c) Give the IUPAC name of the structure shown. (d) Give the IUPAC name of the structure shown. Provide stereochemical descriptor(s) as needed. (e) Give the IUPAC name of the structure shown. 3

4 Question 3. Conformations of Alkanes. (20 points) (a) Provide Newman projections of the staggered (left) and eclipsed conformations of ethane. (4 p.) (b) Three models are shown of butane. 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. (6 points) (c) Structures are shown of 1-tert.-butyl-4-chloro-cyclohexane. 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. (10 points) 4

5 Question 4. Combustion Reactions of Hydrocarbons. (20 points) (a) Provide the stoichiometry of the complete combustion of octane to CO 2. (3 points) 2 C 8 H 18 + _ O 2 _ CO 2 + _ H 2 O (b) Provide the stoichiometry of the incomplete combustion of methane to formaldehyde, H 2 CO. (3 p.) CH 4 + _ O 2 _ H 2 CO + _ H 2 O (c) Provide the stoichiometry of the complete combustion of acetylene, C 2 H 2. (3 points) 2 H C C H + _ O 2 _ CO 2 + _ H 2 O (d) 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 unpaired electrons and both O-atoms have an electron (sextet, heptet, octet). (5 points) (e) The first step of the combustion of methane consists in the abstraction of a H atom by O 2. Draw the complete structures of CH 4, O 2 and the reaction products. 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) (a) Draw the structural formulas for all products formed in the chlorination of methane and provide their names. (8 points) (b) Provide the structures of the possible products of monochlorination of pentane. Circle the product that will be formed in the largest amount. (8 points) For two extra-points, give the percentage yield you expect for the major product. (c) Provide the structures of the major products of mono- and dibromination of 2,4-dimethylpentane. monobromination of 2,4-dimethylpentane (2 p.) dibromination of 2,4-dimethylpentane (2 p.) 6