UMass Amherst CHEM 261 - Chem 261 Exam 1 Practice (7 pages)

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Chem 261 Exam 1 Practice



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Chem 261 Exam 1 Practice

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Pages:
7
School:
University of Massachusetts Amherst
Course:
Chem 261 - Organic Chemistry
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1 Rank the following rotational isomers of 1 2 dichloroethane in order of increasing stability least stable to most stable BAD 2 What functional groups are present in the molecule below A nitrile and an ester 3 Rank molecules A B and D in order of increasing pKa of the most acidic proton in each DBA 4 What types of orbitals are used to make bondA in the structure below sp2 sp3 5 Specify the number of primary carbons in compound A 3 6 Which of the following stick drawings A B D E represent a potential structure for C 5 H 12 A B and E 7 Which of the following is a reasonable resonance structure of the molecule in the box below D 8 Which of the following represents the ground state electron configuration of fluorine anion F 1s 2 2s 2 2p 6 9 Which of the following structures contains a ketone functional group A and E only 10 What are the formal charges on atoms A and B respectively in the following structure D A 0 B 1 11 Determine the orbital hybridization states for atoms A B and D A sp 2 B sp 3 D sp 3 12 Which molecule s below contain a nitrogen with a formal 1 charge D only 13 Determine the IUPAC name for the following molecule 4 ethyl 2 3 5 trimethylheptane First determine the parent name for the molecule by counting the number of carbons in the longest chain There are 7 carbons in the longest chain as illustrated below Next determine the suffix Since the molecule fits the general formula C n H 2n 2 it is an alkane and in this case a heptane Next the substituents must be identified and placed in front of the parent name in alphabetical order The three methyl groups are simplified using the number modifier tri 14 What is the IUPAC name of the following compound trans 1 tert butyl 2 methylcyclopentane The positions of the substituents in this case should be assigned to keep the numbers as low as possible 15 What is the best Lewis structure for H 2 CO 3 note charges have yet to be assigned This choice is best because it has octets for all its atoms except H which can share 2 valence electrons max and it is the only choice for which each atom would be uncharged 16 Which of the following statements is false concerning resonance structures Each atom in a contributing structure must have a completed valence shell While a structure in which all the atoms have filled valence shells will certainly contribute more to the resonance hybrid than those with one or more incomplete shells resonance structures can be drawn where an octet is not satisfied The example below illustrates how carbon can sometimes possess only 6 valence electrons and thus behave in a manner consistent with positively charged atoms 17 Which statement best describes this reaction An acid base reaction where NH 3 acts as a Lewis base In order to answer this question we first need to know the Lewis structures of the molecules in question Using rules learned in chapter 1 we can see that NH 3 possesses a lone pair of electrons while AlH 3 does not Since no protons where gained or lost from either molecule neither of them can be Br nsted Lowry acids or bases However we do see that NH 3 donates its two electrons to form the new N Al bond We know that it is NH 3 that donates the electrons because AlH 3 does not have electron pairs to donate 18 Which one of the following structures represents a different compound from the other three 3 19 Which of the following compounds A B D E have a dipole moment BD 20 How many sigma bonds are there in the compound below 10 21 Which of the following chair structures represents the lowest energy conformation of trans 1 isopropyl 3 methylcyclohexane B 22 Determine the conformational preferences axial or equatorial for the two indicated groups in the lowest energy ring flip of the molecule below A axial B equatorial 23 Which of the following protons H A H B and H D is most acidic HB 24 Which of the following structures represents trans 1 2 dimethylcyclohexane 2 4 11 in Book 25 How many Gauche interactions are present in the molecule below as drawn 2


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