TEST 2 GOC & POC tough by S.K.sinha See Chemistry Animations at sinhalab.com

8/14/2019 TEST 2 GOC & POC tough by S.K.sinha See Chemistry Animations at sinhalab.com

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TEST 2 GOC & POC

1 .For the compound shown below draw three other tautomers and explain why each is

less stable than the tautomer shown.

N

NH

O

2. Explain why imidazole is both a stronger acid and stronger base than pyrrole.

N

NH

NH

imidazole pyrrole 3.Consider Compound A below, and answer the questions that follow.

C C

CH3

C FCH3

CH3

Br

H

H

H

Compound Aa. Put a star (*) by any chirality centers in Compound A.b. Give the IUPAC name for Compound A.c. Draw an enantiomer of Compound A, if one exists. If Compound A does not have anenantiomer, say so.

d. Does Compound A have any diastereomers? If so, how many does it have?e. Does Compound A have an internal mirror plane? If so, indicate where it is.f. A solution of 20.0g of Compound A in 100 mL of water produces a rotation of -40.0

when placed in a 20 cm polarimeter cell. Calculate the specific rotation: show your work.

4. Answer the following questions as TRUE or FALSE. If the answer is false, explain

why it is false, and give an example.

a. If a structure is chiral, it must contain at least one chirality center.b. If a structure contains only one chirality center, it is chiral.c. If a structure has an enantiomer, it also has at least one diastereomer.d. If a structure has a diastereomer, it also has an enantiomer.5. How can you separate a pair of enantiomers?

A. Put them in a polarimeter, and use their optical rotations.B. React them with another chiral molecule, and separate them by recrystallization orchromatography.C. Put them into a separatory funnel, and extract them with water that containsdeuterium, an isotope of hydrogen.

D Put them into a large magnetic field, and separate one to the positive pole, and theother at the negative pole

6. Which of the halide ions is the best nucleophile in water?

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a.Fluoride b. Chloride c.Bromide d.Iodide7. Which carbocation below is the most stable?

A. B. C. D.CH3

CH3

CH3

CH2+

8. Which alkene below is the most stable?

A. B. C. D.

9. In an aqueous solution of pH = 7.0, the amino acid glutamine would be expected to be:A) a fully ionized zwitterion with no net charge.

B) a net positive ion due to protonation of the R group nitrogen.

C) a net negative ion due to deprotonation of the R group nitrogen.

D) a totally neutral molecule with no net charge.

10. For amino acids with neutral R groups, at any pH below the pI of the amino acid, the

population of amino acids in solution will:

A) have positive and negative charges in equal concentration.

B) show no net charge. C) have a net positive charge.

D) have a net negative charge.

11.Titration of leucine by a strong base results in two pKa values. The titration that occurs

atpK2 is:

A) -COOH + OH- -COO- + H2O B) -COOH + -NH2 -COO- + -NH3+

C) -NH3+ + OH- -NH2 + H2O D) -NH2 + OH- -NH- + H2O

12.An octapeptide (GLY-ALA-GLY-ALA-GLY-ALA-GLY-ALA) has:

A) two free amino and two free carboxyl groups.

B) a single free amino group on an alanyl residue.

C) a single free amino group on an alanyl residue and a single free carboxyl group on a

glycyl group.

D) a single free amino group on a glycyl residue and a single free carboxyl group on analanyl

residue.13.What will be the net charge of the tripeptide, LYS-HIS-TYR at pH 7.0?

A) +1B) 0 C) -1D) -2

14 Amino acids commonly found in turns and loops are:

A) ALA and GLY. B) PRO and GLY.

C) two CYS. D) those with ionizable R groups.




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Problem 15: Natures building blocksNatural rubber is a polymer composed of isoprene, the conjugated diene 2-methyl-1,3-butadiene. Isoprenecan be found not only in rubber but in a wide range of natural products called terpenes, most of which havecarbon skeletons made up of isoprene units joined head-to-tail. Recognition of this fact - the isoprene rule -has been great help in working out structures and determining the biosynthetic origin of terpenes.15-1. Find the isoprene units in the following terpenoid natural products.

OH OH

O

OH

O OH OBz

OAcO

R

O

OAc

In polymer chemistry, the repeating unit is called a monomer and the repeating units are joined togetherthrough chain reaction polymerization or step-reaction polymerization. A few examples of step-reactionpolymerization are provided below.

15-2. Draw the repeating unit in each polymer product.

HOOCCOOH

+

H2NNH2

saltheat

Nylon-6,6

O

O

O

+ HO OH

OH

heatGlyptal

NCO+ HO Polyurethane

NCO

OH



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TEST 2 GOC & POC tough by S.K.sinha See Chemistry Animations at sinhalab.com