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850Exam-1 - NAME CEM 850 Exam-1 This exam consists of 16...

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NAME: 1 CEM 850 Exam-1 September 20, 2003 This exam consists of 16 pages including the Table at the end. Be sure to write your name on all pages of the exam. Please write legibly and draw all structures clearly. Good luck. 1. (10 pts) Consider the following eight representations of brominated hydrocarbons: CH 3 CHBrCH=C(CH 3 ) 2 (CH 3 ) 2 CHCH=CHCH 2 Br H CH 3 H 3 C H H Br 1-Bromo-3-methylcyclopentane 2-Bromo-2,2-dimethylpropane 2-Bromo-4-methyl-4-pentene A B D C F H E G Br Br In this collection, identify… a) Two compounds that could have cis and trans isomers: ______ and ______. b) A chemically meaningful but IUPAC incorrect name: ______; write the correct name here: _________________________________________________. c) A chemically impossible structure (violates octet rule): _______. d) Two representations of the same compound: ______ and ______. e) All but one of the chemically reasonable structures [i.e. not the answer to question (c)] have the same formula, which is: ___________. Which is the one with a different formula (hint: think of degrees of unsaturation): ______.
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NAME: 2 2. (10 pts) (a) (1 pt each) Form acceptable Lewis structures for the following uncharged compounds by adding the necessary nonbonding electrons and multiple bonds: N H N C O H H H H C N (b) (1 pt each) Assign charges (if any) to the atoms in the following structures: B H H H H O N O (c) (2 pts) Among the three proposed resonance structures below, one is not acceptable. Circle the bad structure and briefly explain what's wrong with it. H 2 C N O O H 2 C N O O H 2 C N O O Explanation:
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NAME: 3 (c) (4 pts) Ions H 2 + and He 2 + have similar bond strengths (ca. 60 kcal/mol) but neutralization of their positive charges by adding an electron results in bond strengthening for one and dissociation for the other. Label the simple MO interaction pictures below, and use them to help explain the similarity of the cations and the difference between the neutral systems.
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