UMass Amherst CHEM 261 - Organic Chemistry Exam 2 Practice Answers 261 (10 pages)

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Organic Chemistry Exam 2 Practice Answers 261



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Organic Chemistry Exam 2 Practice Answers 261

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Pages:
10
School:
University of Massachusetts Amherst
Course:
Chem 261 - Organic Chemistry

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1 Rank the following substituents from lowest to highest priority according to the Cahn Ingold Prelog rules CIP rules rank groups based on their atomic number The atom with the lowest atomic number is the lowest group and the atom with the highest number is the highest priority C 6 O 8 H 1 N 7 I 53 O 8 CHI3 53 6 7 166 OH 8 1 NH2 7 1 1 9 BEDA 2 Which of the following structures are meso compounds A and E only A meso compound is a stereoisomer and thus by default must have a stereocenter Meso compounds require at least two stereocenters A compound with only one stereocenter cannot be considered a meso compound as it would not be achiral and would not have another stereocenter to oppose its optical behavior See if the molecule has an internal mirror plane Any molecule can have stereoisomers but not all have internal mirror planes The mirror plane should bisect the molecule Ensure that both halves are in fact mirror images of each other The meso compound must be symmetric about the internal mirror plane Each opposing stereocenter must have differing absolute configurations and the attachments on each stereocenter must be the same If the opposing stereocenters have the same absolute configurations or the attachments on either side are different then one half will not be a mirror image of the other half 3 Specify the number of Chiral Centers in the molecule below Chiral molecules usually contain at least one carbon atom with four nonidentical substituents 3 4 What is the relationship between molecules A and B They re Constitutional isomers Diastereomers sometimes called diastereoisomers are a type of a stereoisomer Diastereomerism occurs 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 Enantiomers are chiral molecules that are mirror images of one another Furthermore the molecules are non superimposable on one another This means that the



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