Part 5: STRUCTURE DETERMINATION

Note that there is no point showing all possible answers here, so the most likely and potentially simplest answers are shown.

a. 104.08 g/mol (1.5 marks)

Solution : C₄H₅FO₂ has a molecular weight (6 x 12.01) + (10 x 1.008) + (2 x 16.00) = 104.08 g/mol

b. 2 (1.5 marks)

Solution : the formula for index of hydrogen deficiency, IHD = 0.5 ( 2c+2-h), therefore, the IHD = 0.5 (2 x 6 + 2 - 10) = 2

c.

(3 marks)

Solution : cis-alkene (based on root chain shape) soluble in NaHCO₃ suggests carboxylic acid : solubility expt.

di.

(4 marks)

Solutions : draw a cyclic ester with a chirality center (i.e. it has an sp³ C with 4 different attached groups) using wedge-hash representation. CIP priorities of the example are shown 1-3, assume the H is back and is "4" . Clockwise implies "R"

ii. Shown in figure above. Review Cahn-Ingold-Prelog priority rules (2 marks)

iii. Shown in figure above. Review assigning configuration (1 marks)

Common errors:

• did not calculate MW correctly
• incorrect IHD calculation (e.g. forget to divide by 2 or didn't read the MF correctly)
• not understanding that isomers are molecules with the same molecular formula
• drawing structures that violated the rules of valence
• in part d didn't understand a chirality center (e.g. assigning an sp2 C in an alkene or carbonyl as being chiral or not having 4 different groups attached to an sp3 C. (ii) couldn't apply the Cahn-Ingold-Prelog rules to assign configuration correctly (nomenclature !)