Recitation__3_Sept_9_ANSWERS - Organic Recitation #3 Sept...

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Unformatted text preview: Organic Recitation #3 Sept 9, 2007 Chemistry 357 - Qatar Organic Chemistry for the Life Sciences Recitation Exercises - ANSWERS 1. A) CIRCLE the structure having the LOWEST boiling point. CH 3 CH 2 SH CH 3 CH 2 OH b p = 3 5 o C b p = 7 8 o C EXPLAIN: Simply speaking, ethanol forms strong intermolecular O H bonds where ethanethiol does not form H-bonds (or forms very weak ones). Stronger intermolecular bonds (e.g. H- bonds) increases the boiling point. However, to get FULL MARKS , a more complete explanation is needed. Oxygen has very high electronegativity (3.5) and therefore the O-H bond is very polar (electronegativity of hydrogen (2.1). Since the difference between the electronegativities is quite large ( = 1.4), strong H-bonds are observed. However, sulfur is much less electronegative (2.6) relative to oxygen making the S-H bond much less polar ( = 0.5). Ethanethiol has negligible H-bonding and therefore, has a lower boiling point. B) RANK the boiling points ( 1 = HIGHEST and 3 = LOWEST ) for the following compounds. CH 3 CH 3 CH 3 OH CH 3 CH 2 CH 2 CH 2 CH 2 OH 1 2 3 C) CIRCLE the structure that is a SKELETAL ISOMER of 3-hexanone. O O O 3-hexanone Positional Isomer Functional Isomer O 2. Above each IUPAC name, provide a skeletal or line structure for that compound. O H O O A) 3-methyl-4-phenyl-1-butene B) 3-(1,3-dimethylbutyl)-1,4-pentadiene C) cyclopropylmethanal D) 3-methylphenyl propanoate...
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Recitation__3_Sept_9_ANSWERS - Organic Recitation #3 Sept...

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