CH 2230 test 2
A newly isolated natural product was shown to be optically active. If a solution of 2.0 g in 10 mL of ethanol in a 50 cm tube gives a rotation of +2.57°, what is the specific rotation of this natural product?
+2.57
1) What type of isomers are CH3CH2OCH3 and CH3CH2CH2OH? A) constitutional B) symmetrical C) configurational D) conformational E) stereochemical
A
19) Which of the following halides is least reactive in an E2 reaction with sodium methoxide? A) (CH3)3CCH2I B) (CH3)2CHCHICH3 C) (CH3)2CHCH2Br D) (CH3)2CHCH2Cl E) (CH3)2CHCH2CH2Cl
A
6) Which alkyl halide reacts the fastest in an E2 reaction? A) 2-chloro-2-methylbutane B) 1-chlorobutane C) 1-chloro-2-methylbutane D) 2-chlorobutane E) chloromethane
A
Which of the following statements correctly pertains to a pair of enantiomers? A) They rotate the plane of polarized light by exactly the same amount and in opposite directions. B) They rotate the plane of polarized light by differing amounts and in opposite directions. C) They rotate the plane of polarized light by differing amounts and in the same direction. D) They have different melting points. E) They have the same melting point, but they have different boiling points.
A
18) Which of the following halides is most reactive in an E2 reaction with sodium methoxide? A) (CH3)3CCH2I B) (CH3)2CHCHICH3 C) (CH3)2CHCH2Br D) (CH3)2CHCH2Cl E) (CH3)2CHCH2CH2Cl
B
If (S)-glyceraldehyde has a specific rotation of -8.7°, what is the specific rotation of (R)-glyceraldehyde? A) -8.7° B) +8.7° C) 0.0° D) cannot be determined from the information given
B
Which of the following statements is true concerning the E2 reactions of alkyl fluorides? A) Alkyl fluorides react more readily in E2 reactions than do alkyl iodides. B) The transition state of this E2 reaction resembles a carbanion rather than an alkene. C) The C-F bond is the weakest carbon-halogen bond so SN2 will always predominate over E2 in the reactions of alkyl fluorides. D) Alkyl fluorides react to form the most stable carbocation intermediate. E) Alkyl fluorides cannot adopt the proper stereochemical alignment for an E2 reaction to occur.
B
5) What is the most reactive alkyl halide for elimination reactions? A) 1-chlorobutane B) 1-fluorobutane C) 1-iodobutane D) 1-bromobutane
C
1) Which of the following are the elimination products of the reaction shown below? CH3CH2Br + -OH → ? A) CH3CH2Br+H + O- B) HOCH2CH2Br C) CH3CH2OH + Br- D) CH2CH2 + Br- + H2O E) CH2CHBr + H2O
D
7) Which of the following cannot exhibit chirality? A) 2, 3-dibromobutane B) 1, 3-dibromobutane C) 1, 2-dichlorobutane D) 1, 4-dibromobutane E) 1-bromo-2-chlorobutane
D
A mixture of equal amounts of two enantiomers ________. A) is called a racemic mixture B) is optically inactive C) implies that the enantiomers are meso forms D) both A and B E) none of the above
D
When 2-bromo-3-methyl-1-phenylbutane is treated with sodium methoxide, why is the major product 3-methyl-1-phenyl-1-butene? A) SN2 predominates over E2. B) E1 predominates over E2. C) The bulkiness of the methoxide results in the less substituted alkene. D) The newly formed double bond in this compound is conjugated with the phenyl ring. E) The less substituted alkene is always more stable than the more substituted alkene.
D
Which of the following is a true statement? A) All chiral molecules possess a plane of symmetry. B) All achiral molecules are meso. C) All molecules which possess a single chirality center of the S configuration are levorotatory. D) A mixture of achiral compounds will be optically inactive. E) All molecules which possess two or more chirality centers will be chiral.
D
Which of the following is not true of enantiomers? A) They have the same melting point. B) They have the same boiling point. C) They have the same chemical reactivity with non-chiral reagents. D) They have the same density. E) They have the same specific rotation.
E
Which of the following is/are optically inactive? A) a 50-50 mixture of R and S enantiomers B) a meso compound C) every achiral compound D) a racemic mixture E) all the above
E
The compound CH3CHClCH2CH=CHCH2CH3 contains only one asymmetric center. Explain why it has four stereoisomers.
In addition to the single asymmetric center which may be either R or S, it also contains a carbon-carbon double bond which may be either E or Z. Thus, the four stereoisomers can be designated E, R; E, S; Z, R; and Z, S.
When 1-iodo-1-methylcyclohexane is treated with NaOCH2CH3, the more highly substituted alkene product predominates. When KOC(CH3)3 is used instead, the less highly substituted alkene product predominates. Offer an explanation.
The unhindered ethoxide produces the more stable alkene product (ie, the more highly substituted alkene possible). When the bulky t-butoxide is used, the most accessible hydrogen is removed. This results in the least highly substituted alkene possible.
conformational
a form of stereoisomerism in which the isomers can be interconverted exclusively by rotations about formally single bonds
constitutional
compounds that have the same molecular formula and different connectivity
enantiomer
each of a pair of molecules that are mirror images of each other.
configurational
stereoisomers that can cannot be converted into one another by rotation around a single bond
diastereomers
when two or more stereoisomers of a compound have different configurations at one or more (but not all) of the equivalent (related) stereocenters and are not mirror images of each other.
