Joe 1. chemist is stressed out about his Chem 281 midterm and in the 281 lab mixes together the chemicals A, B, C and D (below) from a few different labs. Before his TA finds out he attempts to separate these chemicals by distillation but mistakenly sets t e heating element to 180 C. Before he h realizes his mistake, 3 of the compounds have distilled!
O OH HO OH Cl
A
B
C
D
a) Which compounds distilled (from lowest to highest boiling) (4 marks) lowest boiling highest boiling
b) He then takes this new mixture of three compounds and adds it to a separatory funnel containing water and pentane. Please indicate on the diagram below in which layer (pentane or water) each of the three compounds will be found (you should end up with 3 empty boxes!). (4 marks)
compound(s) in water layer compound(s) in pentane layer
c) Now, he takes a small sample from the pentane layer of the separatory funnel and places it on a TLC plate that contains a standard sample of butanoic acid (as indicated). After the plate has been placed in a jar of pentane and the pentane has been drawn up the plate by capillary action he finds that the compounds that were in the pentane layer of the separatory funnel have separated, or run up the TLC plate at different rates. Using the new position on the plate of the butanoic acid as a reference, in the dashed box please draw and label with the appropriate letter (roughly) where you would expect the remaining two compounds to be. (DON'T WORRY ABOUT WHERE PENTANE WOULD BE) (4 marks)
TLC plate jar with pentane butanoic acid unkown mixture allow pentane to rise up plate butanoic acid
2. In each series below, please circle the molecule with the SMALLEST bond angles. (2 marks each) a) b) C2H6 BH3 C2H4
C2H2
y
NH4
CH3
3. Consider the neutral molecule below (2 marks for each of a) to e)):
NH3 O O O
__________ __________
a) how many lone pairs of electrons are in this molecule? b) how many sp hybridized atoms are in this molecule? c) circle the atom/atoms that bear a charge.
d) circle the atomic orbitals below that are involved in forming the alkyne bond. Px Py Pz
sp
sp2
sp3
d5 __________
e) how many hydrogen's are in this molecule?
4. Please draw the following four molecules (2 marks each) a) 3,5-diethyl-4,4-dimethylheptane
b) (2S,3R)-3-hydroxy-2-(1-methylethyl)-1-cyclopentanone
2
Question 4 continued......... c) 3-methyl-2-(1-methylethyl)-butanal
d) (3R,4R)-4-bromo-3-methyl-3-hexanol
5. Common table sugar is another name for the OH naturally occurring organic molecule sucrose, which sweet tastes at concentrations HO OH GREATER than 3 mg/mL. One morning Joe O OH chemist is making a cup of coffee (for those O O HO of you that stay out of the kitchen a cup = 250 OH mL) but forgets how much sugar he has HO sucrose added. Being an organic chemist, Joe places [] = +60 OH D some of his coffee in a 10 cm long sample tube and places the sample tube in his polarimeter, which then gives an observed specific rotation ( ) of +6 for the sample. (Assume there are no other chiral molecules in his coffee).
a) would his coffee taste sweet? (2 marks) circle
YES
or
NO
b) how much sugar (in g) was added to his cup of coffee? (2 marks)
____________
c) what is the maximum observed specific rotation ( ) for a NON-sweet cup of coffee? (assume that sample is in a 10 cm sample tube) (2 marks)
3
= _______________ 6. a) In the space below, please draw two different stereoisomers of 1,3,5trimethyl cyclohexane as perspective drawings (use wedges and hatched lines). (4 marks)
b) in the space below, please redraw the two isomers from part a) in their most stable, chair conformations. (4 marks)
c) if either/both are chiral please indicate by circling it/them. (2 mark) d) draw a box around the more stable isomer drawn in part a). (1 mark) e) in the space below, draw the less stable chair conformation for the isomer identified in part d). In three words or less, what interactions destabilizes this conformation. (3 marks)
4
7. Consider the following molecules:
OH OH OH
Br
Br
Br
A
B
C
a) in the bracke...