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CHEM 10052Exam #2Name______
Spring 1998ss#______
1)Compare the molecular structure and physical properties of alcohols and thiols. Include descriptions of geometry, orbital hybridization, hydrogen bonding, relative melting points and boiling points, and water solubility. (10 pts.)
alcoholsthiols
Alcohols and thiols have a bent geometry with 109.5º bond angles and are sp3 hybridized. Alcohols are very polar compared to thiols due to the greater electronegativity of the oxygen in these molecules. Alcohols also exhibit good hydrogen bonding properties while thiols are incapable of hydrogen bonding. Consequently, alcohols have comparatively higher melting points, boiling points and densities than thiols. Finally, alcohols are much more water soluble than thiols due to their greater polarity and hydrogen bonding.
2)Compare the molecular structure and physical properties of aldehydes and ketones. Include descriptions of geometry, orbital hybridization, hydrogen bonding, relative melting points and boiling points, and water solubility. (10 pts.)
aldehydesketones
Both aldehydes and ketones are trigonal planar with 120º bond angles and sp2 hybridization. Aldehydes are slightly more polar than ketones and both are more polar than alcohols. While hydrogen bonding is not possible between aldehyde or ketone molecules, both are capable of hydrogen bonding in solvents such as alcohols or water. Aldehydes may have slightly higher melting points, boiling points and densities as compared to ketones. Simple aldehydes and ketones are water soluble.
3)Name the following compounds using either common nomenclature or IUPAC systematic nomenclature (2 pts each).
a) b) c)
3-methylcyclohexanone2-nitropentanal2-butane thiol
d) e)
2-mercaptobenzaldehydecis-2-mercaptocyclopentanol
4) Draw structural formulas for the following compounds (2 pts. each):
a) 2-mercapto-1-butanolb) 2,2-dimethoxypropane
c) 3-pentanoned) 2-heptanol
e) 3-hydroxy-2-methylhexanal
5) Predict the major products for the following reactions (3 pts. ea.)
a)
b)
c) + NaBr
d)
e)
f)
g)
h)
i)
j.)
6) Write a detailed mechanism for the aldol condensation reaction of ethanal (10 pts.).
7) Write a detailed mechanism for formation of acetals starting with acetone (10 pts.).
See notes
8)The following compound can be made by a mixed aldol reaction between two different carbonyl compounds. What two starting materials would you use? (4 pts)
AB
9)The amino acid cysteine forms a disulfide when oxidized. What is the structure of this disulfide? (3 pts)