Multiple Choices



Multiple Choices

11) Which of the following molecules will absorb IR radiation?

H2O N2 CH4 O2 CO2 NO

a) N2, CH4, CO2, NO only

b) H2O, CH4, CO2, NO only

c) H2O, CH4, CO2 only

d) All of the gases

12) The infrared spectrum below is most likely to be that of a member of which homologous

series?

|C-Cl stretching vibrations 600 - 800 cm-1 |

|O-H stretching vibrations 2500 - 3300 cm-1 |

|C=O stretching vibrations at 1680 – 1740 cm-1 |

a) alcohol

b) chloroalkane

c) aldehyde

d) carboxylic acid

13) The correct order for the basic features of a mass spectrometer is

a) acceleration, deflection, detection, ionization

b) ionisation, acceleration, deflection, detection

c) acceleration, ionisation, deflection, detection

d) acceleration, deflection, ionisation, detection

14) Which of the following will give a molecular ion having m/z = an odd number?

a) CH3CH2OH

b) CH2BrCl

c) CH3CH2NH2

d) (CH3)2NCH2C N

15) The molecular formula for compound A is C5H10O. From the mass spectrum below, Compound A is a _________________:

a) Alcohol

b) Aldehydes

c) Ketones

d) Carboxylic acid

16) The reaction between methane and chlorine will produce chlorometane and hydrochloric acid. This is an example of ______________ reaction.

a) Substitution

b) Elimination

c) Addition

d) Oxidation

17) The first step in any reaction is the breaking of the bonds. Referring to the mechanism below, the type of bond breaking that involve in this reaction is

a) Hemolytic bond breaking

b) Heterolytic bond breaking

c) Homolytic bond breaking

d) Homolytic and heterolytic bond breaking

18) All of the characteristics below are referring to one of the reagents in organic chemistry. The respective reagent is

i) Atom or a group of atoms that is attracted to an electron-deficient centre

ii) Atom where it donates a pair of electrons to form a new covalent bond

iii) They maybe negatively charged ions

a) Electrophilic

b) Nucleophilic

c) Free radical

d) Electron

19) All of these statements are true about SN1 mechanism except:

a) It is a two stages process

b) It is an electrophilic substitution reaction

c) It involve the formation of carbocation which is a slow process

d) More likely with tertiary (3°) halogenoalkanes

20) Which of the statements is true about ozone?

a) There are two types of ozone which are stratospheric and tropospheric

b) Ozone cannot be depleted naturally

c) Tropospheric ozone is needed for the absorption of UV wavelength

d) The nitric oxide (NO) gas helps in the inhibition of the ozone depletion process

Structure

23) A) Organic reaction mechanisms help to develop an understanding of how and why reactions occur.

(a) Propene reacts with hydrogen bromide by an electrophilic addition mechanism forming 2-bromopropane as the major product.

The equation for this reaction is shown below.

(i) Outline the mechanism for this reaction, showing the structure of the intermediate

carbocation formed (4 marks)

(ii) Give the structure of the alternative carbocation which could be formed in the

reaction between propene and hydrogen bromide. (1 marks)

B) A substitution reaction occurs when 2-bromopropane reacts with aqueous sodium

hydroxide.

(i) Draw the structure of the organic product of this reaction and give its name.

(2 marks)

Structure

Name Propan-2-ol (1)

(ii) Name and outline the mechanism for this reaction. (3 marks)

Name of mechanism : Nucleophilic substitution (1)

Mechanism

24) a) A gaseous sample of an element can be analysed using a mass spectrometer.

i) Write a general equation for fragmentation of a molecular ion M+· into two new species. Explain briefly why only one of these species can be detected. (2 marks)

M+

ii) The diagram below show the mass spectrum for an organic compound which contains carbon, hydrogen and oxygen only. The infrared spectrum of X indicates the presence of C=O group.

e) Identify the ions responsible for the peaks at m/z 29 and 57 (2 marks)

m/z 29 = +COH / +C2H5 (1) and m/z = 57 = C3H5O+ (1)

b) Which homologous structure does compound X belongs to? (1 marks)

Aldehyde (1)

f) The infrared shown below is that of compound X which has the molecular formula C4H8O2.

i) What is the bond responsible for the absorption marked Y? (1 m)

Y = C-H bond (1)

ii) Draw two structures of carboxylic acids having the molecular formula C4H8O2 and explain why X cannot be either of them. (3 marks)

CH3CH2CH2COOH and (CH3)2CHCOOH ( 1 mark for each structure)

- No broad band responsible to the O-H bond around 3300 – 3250 cm-1 (1)

iii) Give two analytical uses of infrared spectroscopy. (1 marks)

• Identification of particular bonds in a molecule

• Identification of compounds by direct comparison of spectra

• Or any relevant answer

• ½ mark for each answer.

-----------------------

+

( 1 )

100

Relative Intensity

m/z

M1+

M2·

Only one carries positive charge while the other is radical. (1)

(1)

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download