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PORTAGE CHEM 219 UNI T 3,
ORGANIC CHEMISTRY MO DULE 3,
FINAL EXAM CHEM 219, CHEM 219
EXAM 1
Question: How do the differences caused by
stereoisomers differ from the differences caused by constitutional isomers?
Correct answer: While the structural differences between
stereoisomers are more subtle than those between constitutional isomers, stereoisomerism is often responsible for significant differences in the chemical and physical properties of organic compounds, including the biochemical behavior of many compounds such as drug molecules, amino acids, carbohydrates, and nucleic acids.Several of the human senses, especially smell, are greatly affected by stereoisomerism in organic compounds.
Question: What test can be applied to determine if an
object is chiral or achiral?
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Correct answer: A simple test involves comparing the
object and its mirror image for superimposability.
Question: What does it mean when a molecule is a chiral
molecule?
Correct answer: An organic compound that can exist as
two different forms ("left-handed" form or a "right- handed" form).
Question: Is lactic acid structure chiral or achiral?
Correct answer: Attempting to superimpose lactic acid
and its mirror image reveals that the two forms cannot be superimposed, and thus, the molecule is chiral, and it exists as two separate forms known as enantiomers.
Question: Is the molecule 2-chloropropane chiral or
achiral?
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Correct answer: The absence of a stereocenter is the
reason why molecules like 2-chloropropane are achiral.An analysis of the 3D structure of 2-chloropropane reveals a tetrahedral geometry around the central carbon but only three different types of atoms or groups attached (there were 4 bonds to the carbon but 2 of the groups were identical). The symmetrical nature of the 2- chloropropane molecule comes from having two of the same group on the central carbon - this allows the structure to be superimposed on its own mirror image, and thus, makes the molecule achiral.
Question: What is the most common cause of chirality in
an organic molecule?
Correct answer: The presence of a tetrahedral
stereocenter.
Question: What are two things that rule out a carbon from
being a stereocenter?
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Correct answer: - if the carbon has more than one
hydrogen on it (makes it so there can't be four different groups/atoms)
- if the carbon has a double or triple bond (makes it so
there can't be four separate bonds and therefore can't have tetrahedral geometry)
Question: How is the presence of a stereocenter in an
organic structure denoted?
Correct answer: With an asterisk next to the stereogenic
carbon.
Question: Look at the image of 3-methylhexane and
explain whether it has a stereocenter and why?
Correct answer: Yes, it is chiral because it has a
stereocenter. The substituents attached to carbon #3 are a methyl, an ethyl, a propyl, and a lone hydrogen (not pictured). While methyl, ethyl, and propyl are all carbon-