Homework 3 (MOL S11) - ANSWERS

Homework 3 (MOL S11) - ANSWERS - V55.0310 NATURAL SCIENCE...

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1 V55.0310 NATURAL SCIENCE II: MOLECULES OF LIFE SPRING 2011 HOMEWORK 3 - ANSWERS DUE AT THE BEGINNING OF CLASS ON WEDNESDAY, FEBRUARY 23 Name : _________________________________ __ Lab section and Time : _________________ Lab Instructor: _______________________________ Answer all questions on this sheet in the space provided. Two questions will be graded with a maximum of four points each. Two extra points will be awarded for completing all the questions. HYDROCARBONS Question 1: Butane is an alkane hydrocarbon with the formula C 4 H 10 . Consider the isomer n- butane where all the carbon atoms form a linear chain. Draw the following structures for n-butane: (a) The Lewis dot structure. CC : : : : . . . . . . . . . . . . . . . . : H H H H H H H H H H Lewis dot structure (b) The two-dimensional structure. 2D structure H H H H H H H H H H (c) The three-dimensional structure (viewed from the side) C C C C 3D structure H H H H H H H H H H
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2 NOTE: The most common error in drawing 3D structures of hydrocarbons such as butane is to draw all of the carbon atoms in a straight line . This is incorrect because it does not accurately represent the tetrahedral geometry of the 4 bonds around the two carbon atoms in the middle of the molecule. The most favorable (lowest energy conformation) of the methyl groups at each end of the molecule will be staggered with respect to the C—H bonds on the adjacent carbon atoms. However, for the purpose of this question I am not too concerned about the staggered/eclipsed geometry of the methyl groups as long as you have the carbon geometry drawn correctly. Question 2: Pentane is an alkane hydrocarbon with chemical formula C 5 H 12 . Use carbon-only structures to draw all of the different structural isomers of pentane. How many unique structural isomers exist for this molecule? [Hint: Look carefully at your drawings to make sure all of your isomers are distinct – i.e., they cannot be interconverted simply by rotating them in 3D space] CCCC isomer 1 CC isomer 1 C C or C C C C C CCC C C isomer 3 C This structure is NOT considered a unique isomer because it has 4 carbons in the longest continuous chain and thus is identical to isomer 1 Question 3 : Pentene is an alkene hydrocarbon with chemical formula C 5 H 10 . One isomer of pentene has the C=C double bond between carbon atoms numbered 2 and 3 (counting from the left). Draw carbon-only structures for the cis and trans isomers in pentene. Make sure that your structure drawings clearly distinguish between the two isomers.
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This note was uploaded on 11/07/2011 for the course MAP V55.0310.0 taught by Professor Tracejordan during the Spring '11 term at NYU.

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Homework 3 (MOL S11) - ANSWERS - V55.0310 NATURAL SCIENCE...

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