Exam November 2014, questions PDF

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School of Chemistry and Biochemistry

SEMESTER 1, 2014 EXAMINATIONS CHEM1002 Chemistry: Structure and Reactivity FAMILY NAME: ____________________________ GIVEN NAMES: ______________________

STUDENT ID:

SIGNATURE: ________________________ This Paper Contains: 21 pages (including title page) Time allowed: 2 hours 10 minutes

INSTRUCTIONS: Section A: Section B:

20 questions (Multiple Choice) 18 questions

TOTAL MARKS: 120

PLEASE NOTE Examination candidates may only bring authorised materials into the examination room. If a supervisor finds, during the examination, that you have unauthorised material, in whatever form, in the vicinity of your desk or on your person, whether in the examination room or the toilets or en route to/from the toilets, the matter will be reported to the head of school and disciplinary action will normally be taken against you. This action may result in your being deprived of any credit for this examination or even, in some cases, for the whole unit. This will apply regardless of whether the material has been used at the time it is found. Therefore, any candidate who has brought any unauthorised material whatsoever into the examination room should declare it to the supervisor immediately. Candidates who are uncertain whether any material is authorised should ask the supervisor for clarification.

Supervisors Only – Student left at:

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SECTION A ; Questions 1- 20 Mark your answers on the sheet provided

1.

Which of the following is the best definition of stereoisomerism?

A.

Molecules that have the same numbers and kinds of atoms connected in a different sequence.

B.

Molecules that have the same arrangement of atoms, but different electronic structures.

C.

Molecules that have the same mass, but different atom types.

D.

Molecules that have the same connectivities, but different 3-D arrangements of atoms.

E.

Molecules that have different isotopes of the same atoms.

2. Which of the following is a valid set of quantum numbers for a unique electron in an atom? A.

n = 4, l = 2, ml = 0, ms = 0

B.

n = 2, l = 2, ml = 0, ms = -½

C.

n = 3, l = 1, ml = 0, ms = 0

D.

n = 2, l = 1, ml = 1, ms = -½

E.

n = 3, l = 1, ml = 2, ms = -½

3. The noble gases all have similar physical and chemical properties. Which of the following provides the best explanation for this observation about these elements? A.

They are all in the same period

B.

They all have a fully occupied valence shell

C.

They are all electropositive

D.

They all have p-orbitals

E.

They are all non-metals

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4.

The formal charges on the atoms indicated in bold are, respectively:

A. +1, +1, –1

B. 0, +1, +1

D. +1, –1, 0

E. 0, +1, –1

C. 0, 0, +1

5. Which of the following conformations of dichloroethane would you expect to be lowest in energy? Cl H

a.

H

H Cl

H

H H

b.

H

H Cl

Cl

HCl c. H

H

HCl

Cl Cl d. H

H

HH

A.

conformation a

B.

conformation b

D.

conformation d

E.

conformations a and b have equally low energy

6.

C.

conformation c

How many sp2 hybridised carbon atoms does the molecule represented below contain?

O

A.

1

B.

3

D.

7

E.

9

C.

5

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7.

What is the relationship between the molecules represented below?

A.

They are a pair of enantiomers

B.

They are diastereomers

C.

They are both achiral

D.

They are identical molecules

E.

They are both meso compounds

8. Which of the alkyl halides (A-E) leads to the product shown (as the major product) below, in an E2 reaction?

H A

Cl

Cl Cl

C

B

E

D Cl

Cl

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9.

Which of the following statements about organic reactions is INCORRECT?

A. Most organic reactions involve the flow of electrons from a full molecular orbital to an empty molecular orbital. B. Orbitals must overlap for a reaction to occur C. Most molecular collisions do not result in a reaction D. In polar reactions, electrons flow from a nucleophile to an electrophile E. Nucleophiles donate a pair of low energy electrons; electrophiles have a vacant, highenergy orbital.

10.

Which of the following reaction mechanisms is INCORRECT or INCOMPLETE?

11.

Which structure best represents the product of the following reaction?

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12.

Which structure represents the major product of the reaction of 1,4-diphenylbutyne with

hydrogen in the presence of Lindlar catalyst?

13.

Which of the following structures DOES NOT represent an aromatic compound?

14.

Which of the following structures DOES NOT represent a coloured compound?

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15.

Which of the following reactions is least likely to give t-butyl methyl ether

?

(Note: HClO4, perchloric acid, is a very strong acid. The conjugate base, perchlorate, is nonnucleophilic.)

16.

Which of the following statements about benzene is INCORRECT?

A.

Benzene undergoes substitution reactions, not addition reactions.

B.

Carbon-carbon bond lengths in benzene alternate between the lengths for C=C and C–C bonds.

C.

All the bond angles in benzene are equal.

D.

The heat of hydrogenation of benzene is considerably less than that expected for the hypothetical compound 1,3,5-cyclohexatriene.

E.

The benzene ring is prevalent in nature as a result of its special stability.

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17.

Select the option A–E representing the expected major product of the following

reaction?

18.

Arrange the following carboxylic acid derivatives in order of increasing rate of hydrolysis (slowest first, fastest last).

A.

I, II, III

B.

I, III, II

C.

II, I, III

D.

II, III, I

E.

III, I, II

19.

Which of the following statements about nucleic acids is INCORRECT?

A.

A nucleoside is composed of a sugar and an amine base

B.

DNA structure is stabilised by base pairing

C.

RNA and DNA both contain glycosidic bonds

D.

Uracil is found in DNA and thymine is found in RNA

E.

RNA is chiral

20. How many possible stereoisomers are there of the Pt(II) coordination compound [Pt(NH3)2(CN)2]? A.

1

B.

2

C.

3

D.

4

E.

can’t be determined with information available

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SECTION B ; Questions 1-19 Mark your answers in the spaces provided below 1. (a) Complete the molecular orbital diagram for ground state He2 by adding the appropriate arrows representing electrons to the empty molecular orbitals. (2 marks)

(b) Showing your working, what is the bond order of the  bond in ground-state He2? (2 marks)

Bond order =

(c) Which is more stable? The  bond in a ground-state He2 molecule, or the  bond in a ground state He2+ ion? (1 mark)

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2. The following drawing describes the valence bond model of bonding in formaldehyde (H2C=O). The drawing requires six labels to be written in the empty boxes A-F. Select from the list of labels given below, and write them in the appropriate boxes. (3 marks)

3. Draw the structures of the two ring-flipped chair conformations of trans-1,4-cyclohexanediol and circle the preferred chair conformation.

(5 marks)

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4.

Identify any stereogenic carbon atoms in the following compounds. Clearly mark them with an asterisk and assign their configuration using the R/S convention. (3 marks)

Can you assign these compounds as (+) or (-) based on their structure? Briefly give your reasoning. (2 marks)

5. 1-Butanol (shown below) has the molecular formula C4H10O. Draw the other six constitutional isomers of formula C4H10O. Draw a circle around any chiral molecule(s). (4 marks)

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6. Fill in the missing reagent(s) in the boxes below. (7 marks)

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6.

continued...

7. A student treated ethyl amine (CH3CH2NH2, liquid) in hexane (solvent) with hydrogen bromide (gas). Explain briefly what would happen in this experiment. What product did they synthesise and visually what would happen? (2 marks)

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8. Predict and draw the structure of the product of each of the following reactions in the boxes provided. (5 marks)

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9.

In the boxes provided, draw the structure of the product or starting material for each of the following reactions. Be sure to clearly indicate the stereochemical configuration where appropriate. (12 marks)

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10. Assign each of the pKa values, –5, 5, 10, 15, to a matching compound (one to each) by writing the number under the appropriate structure. (2 marks)

11. Circle the structure representing the compound that WOULD NOT cause an increase in pH when dissolved in water. (1 mark)

12. Write the mechanism of the electrophilic aromatic substitution of benzene using the nitronium ion (+NO2) as the electrophile. (3 marks)

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13. Write the mechanism of the Grignard reaction of MeMgI with benzaldehyde (PhCHO), followed by acidic workup, to give 1-phenylethanol = PhCH(OH)CH3. (3 marks)

14. Write the mechanism of the reaction of cyanide with benzoyl chloride.

(3 marks)

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15. Illustrated below is a Fisher esterification reaction. By adding the appropriate ‘curly arrows’ and ‘dots’ to represent moving electron pairs, complete the mechanism. (5 marks)

16. Draw the structure of the dipeptide, Gly-Ser formed by the two amino acids serine and glycine in the protonation state expected at neutral pH. Label the two amino acids clearly. Also, label the peptide bond, the amino terminus and the carboxy terminus. (5 marks)

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17. This drawing represents the nucleoside, adenosine. Label the anomeric carbon and the location of the -glycosidic linkage. Draw the structure of 2’-deoxyadenosine. (4 marks)

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18. The following drawing represents the cis stereoisomer of the Pt(II) coordination compound [Pt(NH3)2(CN)2]. Draw the trans stereoisomer in the box. (1 mark)

Draw structural representations of the fac and mer isomers of [Co(H2O)3Cl3] (2 marks)

fac

mer

Circle the correct coordination number of the metal ion in the complex ion [Fe(en)3]3+ (en is an abbreviation for the bidentate ligand, ethyelenediamine). 2

3

4

5

6

7

Explain why there are two stereoisomers of the complex ion [Fe(en)3]3+

(1 mark)

(2 marks)

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