Pusat Pengajian Pendidikan Jarak jauhUNIVERSITI SAINS MALAYSIA

Academic Session:2014/15

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JIK 227 Chemical Spectroscopy –

Due date: 20 April 2015Assignment 2

Lecturer: Associate Prof. Dr. Ab. Rasid Mat Zin

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1.a) What type of informations about an organic compound that could beobtained from :-

i) a UV spectrum

ii) an IR spectrum

iii) a Mass spectrum

iv) a proton NMR spectrum

[10M]

b) Neopentane ion undergoes fragmentation in MS as below.

i) What is the likely structure for ii) Write a balance equation for the formation of C4H9

+ from C5H12+.

[6M]

c) Partial hydrogenation of compound A gives a diene with λmax = 263nm. Suggest a

structure for the diene. Show your calculation.

[4M]

d) Explain how 13C-spectroscopy can be used to distinguish between the ortho-, meta- and para-dibromobenzene isomers from one another.

[4M]

e) Calculate the chemical shift of signals at 875 Hz and at 1775 Hz down field from TMS when measured using 250 MHz spectrometer.

[4M]

2.a) Discuss three different ways how to prepare the samples for the IR spectrum measurement.

[5M]

b) Infrared Spectra ( i) to (iii) below are of p-, m- and o-chlorostyrene isomers. Assign each IR to its correct isomer. Explain your answer.

i)

ii)

iii)

[5M]

c) Predict the appearance of the 1H-NMR spectrum given by the vinyl hydrogen atoms of

p-chlorostyrene below:-

Given,

H(C) 6.7 ; Hδ (E ) 5.3 ; Hδ (D) 5.7δ

J(CD) = 18Hz ; J(CE) =11 Hz ; J(DE) =2 Hz

[5M]

d) Propose a structure for the compound, C8H10, that is consistent with the 1H-NMR data below :-

triplet, δ 1,25 (3H)

quartet,δ 2.68 (2H)

multiplet, δ 7.23 (5H)

[5M]

3.a) Compound B, C11H16, has 1H-NMR and IR spectra as follows. With adequate explanation suggest a structre for B.

1H-NMR spectrum of B

IR spectrum of B

[10M]

b) Compound C, C8H10O, has IR , 1H-NMR and 13C-NMR spectra as follows.With adequate explanation suggest a structure for C.

IR spectrum of C

1H-NMR spectrum of C

13C-NMR spectrum of C

[10M]

4.a) Compound D has IR, MS, 1H-NMR and 13C-NMR as shown below. The MS shows M+ at 136.

Find molecular formula of D and with the aid of other spectra suggest plausible structure for D.

Exact mass = 136.0524.

IR spectrum of D

MS of D

1H-NMR spectrum of D

13C-NMR spectrum of D

[15M]

b) The followig are three 13C-NMR spectra of three isomers of an alkyl bromide with the formula C5H11Br . Assign which spectrum belongs to which isomer.

i)

ii)

iii)

[5M]

5. a) Given below are MS, IR, 1H-NMR and 13C-NMR of a compound E. First, explain each spectrum individually and then consider them in relationto each other before you come out with the structure of E. Exact mass = 113.0841.

MS of E

IR spectrum of E

1H-NMR spectrum of E

DEPT13C-NMR spectrum of E

[15M]

b) ) Given below are MS, IR, 1H-NMR and 13C-NMR of a compound F. First, explain each spectrum individually and then consider them in relationto each other before you come out with the structure of F. Exact mass =138.0681.

MS of compound F

IR of compound F

1H-NMR of compound F

13C-NMR of compound F

[15M]

6. a) Complete the following multiplication table:

E C2

σ

i

E

C2

σ i

[5M]

b) Obtain irreducible representation from each of the following reducible representations

Dapatkan perwakilan tak terturunkan daripada setiap perwakilan terturunkan

berikut:

i)

ii)

(6M)

c) Using unshifted atom method predict IR and Raman activity in [ ICl4]-1 , a D4h molecule .

Show your complete calculation.

[6M]

d) Predict the hybridisation of orbital at the central atom in IF6,

D3d E 2C3 3C2 i 2S6 3σd

5 2 3 -1 2 1 C6v E 2C6

2C3 C2

3 vσ 3 dσ

4 -1

1 2 0 -2

an Oh molecule. Show your complete calculation.

(10M)

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