Examination #1 Bonding, Alkanes, Alcohols & Alkyl Halides. Wednesday, 09/14/05, 11 11:50 am. Answer Key

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1 hemistry 2050 Introduction to rganic hemistry Fall Semester 2005, Dr. Rainer Glaser Examination #1 Bonding, Alkanes, Alcohols & Alkyl alides Wednesday, 09/14/05, 11 11:50 am. ame: Answer Key Question 1. Structural Formula of rganic Molecules 20 Question 2. Atomic Structure, Lewis Structures & Bonding 20 Question 3. Isomers and ombustion 20 Question 4. onformation and Stereoisomers 20 Question 5. Alcohols and Alkylhalides 20 Total 100 1

2 Question 1. Structural Formula of rganic Molecules. (20 points) (a) Draw a complete structural formula of pentane. (4 points) (b) Draw a condensed structural formula of pentane. (1 points) (c) Draw a simplified structural formula (aka bond-line formula) of pentane. (1 points) (d) Provide the complete structural formula and the name of one structural isomer of pentane. (6 p.) Structure: ame: 2-methylbutane (e) Size and shape of acyclic alkanes. (8 p.) Typical length of a single bond: _154_ pm Approximate angle ( ) in acyclic alkanes: > Typical length of a bond: 105_ pm Approximate angle ( ) in acyclic alkanes: > ybridization of in acyclic alkanes: sp 3 Tetrahedral angle:

3 Question 2. Atomic Structure, Lewis Structures & Bonding. (20 points) (a) A neutral oxygen atom contains 8_ protons, 8_ neutrons, _2_ core electrons, and 6_ valence electrons. In the left box, complete the electron configuration of a neutral oxygen atom by provision of the exponents (e.g. the number of electrons in that A). n the right, draw all valence electrons as arrows. (8 points) 1s 2 2s 2 2p x 2 2p y 1 2p z 1 (b) Draw the complete Lewis structures (all atoms, all bonds, all lone pairs, draw all pairs as dashes, use dots only for unpaired electrons, indicate formal charges if any). (6 points) arbon dioxide, 2 itrous Acid, (c) Draw the three important resonance forms of nitrate anion, 3 -. Draw resonance arrows between the structures. Draw complete Lewis structures. (6 points) 3

4 Question 3. Isomers and ombustion. (20 points) (a) Give the molecular formula and the name for the following compound. (4 points) ,2-dimethyl-4-ethyl-hexane (b) Rewrite the condensed structural formula as a bond-line drawing and give its name. (4 points) ( ,2-dimethyl-pentane (c) ircle the isomers. (4 points) butane cyclobutane isobutane 2-methylbutane ( ( 3 2 ( 3 3 ( 2 ) = (d) Provide the reaction formula for the complete combustion of octane (e.g. what happens in your car s engine). (3 points) 3 ( 2 ) _12.5_ 2 _8_ 2 + _9_ 2 (e) Provide the reaction formula for the incomplete combustion of octane. ote that 10 2 are available. [int: ne more product is formed.] (5 points) 5 fewer -atoms, 4 are formed instead of ( 2 )

5 Question 4. onformation and Stereoisomers. (20 points) (a) Draw the perspective drawing of staggered ethane. (4 points) (b) Draw the ewman projection of the trans conformation of butane. (4 points) 3 3 (c) Draw the two chair conformations of ethylcyclohexane in which the substituent is either axial or equatorial. ircle the structure that is preferred. (6 points) Axial ethyl. Equatorial ethyl (d) Draw the best conformation of cis-1-methyl- 4-isobutylcyclohexane. (6 points) ( 3 3 5

6 Question 5. Alcohols and Alkyl alides. (20 points) (a) omenclature. Draw the complete structure of 2-chlorobutane; draw every atom, every bond, every lone pair. (3 points) l Give the IUPA name of the structure shown. (3 points) ame: 2,2-dichloropentane l l (b) When tert.-butanol, ( 3, is treated with l, the first step of the reaction consists in the protonation. Draw the product of this protonation. The next step is the elimination of water and the formation of the tert.-butyl cation. Draw this cation and indicate the hybridization of the central - atom. For both structures, show all atoms, show all lone pairs, show formal charges. (6 points) Protonated tert.-butanol Tert.-butyl cation sp 2 3 (c) omplete the structure of water by adding lone pairs and indicating partial charges on all the atoms. Then draw an arrow that shows the direction of the dipole moment of water (from plus to minus). n the right, again complete the structure of the water molecule shown and then draw a second water that is hydrogen-bonded to water molecule drawn via the hydrogen atom on your right. Try to get the relative distances as right as possible. (8 points) Water Water Dimer δ δ δ 6