Chemistry 29b M. Walker
Practice Test Answer Key
190 points total. Duration 60 minutes. All questions are worth 9 points unless stated. If you believe several answers are possible, choose the best single option.
1. Why is sulfuric acid used along with nitric acid, for the nitration of methyl benzoate?
(a) If nitric acid alone were used, the ester would not protonate and therefore would not dissolve.
(b) Sulfuric acid helps in the generation of the nitronium cation, a key intermediate for the reaction.
(c) Sulfuric acid helps in the generation of the protonated form of the ester, a key intermediate in the reaction.
(d) Sulfuric acid performs a sulfonation reaction, and the nitric acid reacts with the resulting
2. (18 points) In a preparation of 1,4-di-tert-butyl-2,5-dimethoxybenzene (MW 250 g/mol), 304 mg of 1,4-dimethoxybenzene (MP 57 oC, MW 138 g/mol) was reacted with 296 mg of tert-butyl alcohol (MP 26 oC, MW 74 g/mol) in the presence of excess acetic and sulfuric acids.
Part I: What would be the maximum mass of product that could be isolated?
304/138 =
2.20 mmol 1,4-dimethoxybenzene
296/74 = 4.00 mmol tert-butyl alcohol
=> limiting reagent
4.00 mmol t-BuOH => 2.00 mmol product (from equation) => 2.00 x 250
mg
=_500 mg product_______________
Part II: What would be the maximum
mass of product if only 276 mg of 1,4-dimethoxybenzene were used?
Now we have 2.00 mmol dimethoxybenzene. This will still give 2.00
mmol product
=_500 mg product_______________
3. In the preparation of methyl 3-nitrobenzoate, the crude product was washed with ice-cold methanol, which helps to remove water and avoid oil formation during the recrystallization step.
TRUE or FALSE
4. Phenylmagnesium bromide reacts with water to produce the organic product
___BENZENE___
5. When 1,4-dimethoxybenzene, acetic acid and tert-butyl alcohol are mixed then cooled to 0 oC, the mixture forms a thick slush. This is caused by:
(a) Formation of tert-butyl acetate, which is a gelatinous solid.
(b) Formation of 1,4-di-tert-butyl-2,5-dimethoxybenzene which precipitates.
(c) Formation of 1-tert-butyl-2,5-dimethoxybenzene which precipitates.
(d) The tert-butyl alcohol and acetic acid beginning to freeze.
(e) Water produced in the reaction coming out as ice.
6. What is the solvent used for the reaction of diphenylacetylene with tetraphenylcyclopentadienone?
___diphenylacetylene___
7. Aldehydes and ketones can be distinguished using their DNP derivatives, which are always orange for aldehydes and yellow for ketones.
TRUE or FALSE
8. A compound X, of formula C8H8O, forms a highly colored DNP derivative but gives a negative Tollen’s test. Compound X reacts with NaOH/I2 to give iodoform and the sodium salt of a carboxylic acid, Y. The UV spectrum of compound Y indicates that there is no conjugated diene, and the IR spectrum does not contain an alkyne. Draw the structure of X.
_________PhCOMe__________
9. The success of the Fischer esterification usually depends on:
(a) The formation of a stable aromatic system
(b) An ester with a boiling point lower than the starting alcohol
(c) Formation of a silver mirror
(d) Azeotropic removal of water
(e) Fresh carnations left at Fischer’s grave.
10. In the Diels-Alder experiment, which of the following is true?
(a) The high temperatures favor products with higher entropy, and this helps the initial Diels-Alder reaction of diphenylacetylene with tetraphenylcyclopentadienone to form a bicyclic intermediate.
(b) The high temperatures favor products with higher entropy, and this helps drive the collapse of the bicyclic intermediate (with loss of CO) to give hexaphenylbenzene.
(c) The loss of CO is irreversible because it is lost into the air, and this helps drive the collapse of the bicyclic intermediate to give hexaphenylbenzene.
(d) Both answers (a) and (c).
(e) Both answers (b) and (c).
11. To what chemical class does nylon belong?
(a) Amide
(b) Amine
(c) Alcohol
(d) Alkane
(e) Acid chloride
12. What was the base used in the formation of the Wittig reagent in experiment 8?
__Sodium hydroxide__
13. In the preparation of nylon, what remains in the aqueous solution after the nylon strand has been removed?
(a) HCl, and any unreacted diamine
(b) HCl, NaOH and any unreacted diamine
(c) NaCl, NaOH and any unreacted diamine
(d) NaOH only
(e) Thionyl chloride and NaOH
14. The purpose of preparing derivatives (such as dinitrophenylhydrazones) is to provide an additional form of characterization.
TRUE or FALSE
15. What impurity is removed from crude triphenylmethanol (made via the Grignard reaction) using a trituration in petroleum ether?
_____BIPHENYL______
16. (12 points) Isobutyl formate, HCOOCH2CH(CH3)2, is an ester that supposedly smells of raspberries.
Part I: How many types of hydrogen are expected in the NMR spectrum of isobutyl formate?
__________FOUR____________
Part II: What is the multiplicity of each peak in the NMR spectrum?
17. (34 points) Compound X has the formula C10H12O2 and the NMR spectra (1H, 13C) attached. Deduce a structure for X. [1H Spectrum from Univ Potsdam, Ger.]
No. of double bond equivalents = _______FIVE_______
How many types of hydrogen are there below 6ppm? ______THREE_______
How many types of carbon are there? ______EIGHT_______
How many of these carbons are likely to be sp2? ______FIVE______
What no. of hydrogens is present at what chemical shift?
___3H___ at ____2___ ppm ___2H__ at ___2.9___ ppm
___2H___ at ___4.2___ ppm ___5H___ at ___7.2___ ppm
________ at _________ ppm ________ at _________ ppm
________ at _________ ppm ________ at _________ ppm
What prominent groups are present in the 1H spectrum? [Continue overleaf]
Aromatic ring C6H5-
-CH2CH2-O- and CH3
What is the structure of X? Ph-CH2CH2-O-COCH3
Also see a detailed analysis of the H spectrum from the University of Potsdam, Germany.
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