Sindh Mdcat Exclusive Course Chemistry Alkyl Halides And Amines — Solved MCQs

Question 1

Which balanced chemical equation show the formation of ethyl chloride using thionyl chloride?

Accepted Answer

D. CH3COOH + SOCl2 -> CH3COCl + SO2 + HCI — Thionyl chloride is SOCl2 and it reacts with carboxylic acids to form acyl chlorides.Options B and C do not involve thionyl chloride, it mentions SOCl instead of SOCl2 so, they are incorrect.Options A and D are both valid reactions involving thionyl chloride. However, the question asks for the formation of ethanoyl chloride. Option A shows the formation of METHANOYL Chloride, whereby D shows ethanoyl chloride formation so, D is the correct answer.

Question 2

The reduction of nitrile produced a compound of formula C3H7NH2. Which one of the following compounds would be produced if the same nitrile was hydrolyzed by heating with dilute hydrochloric acid?

Accepted Answer

D. CH3CH2CO2H — The hydrolysis of nitrile produces carboxylic acid. Since the number of carbons given in our question is 3 so the correct answer should be a carboxylic acid with 3 carbons and that is option D. A and B are amines, hence wrong. C is wrong because it has extra carbon. E is wrong because it is alcohol.

Question 3

The reaction 2RX + 2Na -> RR + 2NaX is an example of:

Accepted Answer

D. Wurtz reaction — The reaction in the question shows an alkyl halide R-X reacting with Na metal to form a high hydrocarbon along with a compound containing sodium and the halogen.

Question 4

The reaction mechanism of alkanes with halogens is known as;

Accepted Answer

B. Free radical substitution — Free-radical halogenation is a type of halogenation. This chemical reaction is typical of alkanes and alkyl-substituted aromatics under application of UV light and the reaction mechanism is known as free radical substitution. The reaction is used for the industrial synthesis of chloroform (CHCl3), dichloromethane (CH2Cl2), and hexachlorobutadiene. Addition, propagation and elimination are the three steps of free radical substitution.

Question 5

Ethyl iodide and n-propyl iodide are allowed to undergo the Wurtz reaction. The alkane which will not be obtained in this reaction is:

Accepted Answer

B. Propane — In the Wurtz reaction, alkyl halides are treated with metallic sodium or potassium in the presence of an inert solvent such as ether. This reaction leads to the formation of longer carbon chains by coupling two alkyl halide molecules.

Question 6

The order of reactivities of the following alkyl halides for an SN2 reaction is:

Accepted Answer

D. RI > RBr > RCl > RF — The reactivity of the alkyl halide in the SN2 reaction is decided by the ease with which the halide leaves the substrate. The larger the size of the halide ion, the more is the leaving ability. As per the leaving ability, the order is I−>Br−>Cl−>F-. Hence reactivity order is RI > RBr > RCl > RF due to the higher stability of I- ion (due to its higher size). Hence, I ion is easily displaced by a nucleophile.

Question 7

RMgX is an organometallic compound, generally known as:

Accepted Answer

A. Grignard's Reagent — A Grignard reagent of the Grignard compound is a chemical compound with the generic formula R−Mg−X, where X is a halogen and R is an organic group, normally an alkyl or aryl.

Question 8

Catalyst used in reaction CHCl3 + ½ O2 → COCl2 + HCl is _ and its nature is _.

Accepted Answer

B. 2% Ethyl alcohol ... negative — The catalyst in the above reaction is 2% ethyl alcohol with negative nature.

Question 9

Which alkyl halide has the lowest reactivity for a particular alkyl group?

Accepted Answer

B. R-F — To react with the alkyl halides, the carbon-halogen bond has gotten to be broken. Because that gets easier as you go from fluorine to chloride to bromide to iodide, the compounds get more reactive in that order. Iodoalkanes are the most reactive and fluoroalkanes are the least.

Question 10

Zwitter ion is formed when proton goes from:

Accepted Answer

B. Carboxyl to an amino group — Zwitter ion is a dipolar ion which is formed on the combination of a carboxyl group and an amino group. As a result, it is mostly formed by an amino acid. The carboxyl group in a zwitter ion carries a negative charge while the amine group carries a positive charge. There is an internal transfer of a hydrogen ion from the -COOH group to the -NH2 group to leave an ion with both a negative charge and a positive charge. This is called a zwitter ion. This is the form that amino acids exist even in the solid state.

Question 11

R-X on reaction with alcohols form:

Accepted Answer

B. ROR — We can deprotonate the alcohol to form an alkoxide anion RO- which is a much stronger nucleophile and will attack the alkyl halide forming an ether (Williamson Ether synthesis). This usually occurs through the SN2 mechanism.

Question 12

Alkyl halides involving -C-X bond breakage and -C-Nu bond formation simultaneously would follow the mechanism:

Accepted Answer

B. SN2 — The SN2 reaction is a type of reaction mechanism that is common in organic chemistry. In this mechanism, one bond is broken and one bond is formed simultaneously, i.e. in one step. It is a bimolecular reaction because the attacking Nucleophile and the leaving group are both involved in the rate-determining step.

Question 13

NH3 (amine) is an example of:

Accepted Answer

C. Neutral ligand — NH3 is a neutral ligand as it has no charge and can donate a lone pair of electrons to form a coordinate bond with a metal atom or ion.

Question 14

All amino acids contain the functional group:

Accepted Answer

A. NH2 — All amino acids contain an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom and a part where radical attaches.-CO2 is different from -COOH. -CO2 can be present in esters.

Question 15

Ninhydrin reacts with an amino acid to form a product that has the colour:

Accepted Answer

C. Bluish violet — Ninhydrin reacts with the α-amino group of primary amino acids producing 'Ruhemann's purple'. To detect the presence of amino acids , they're made to react with the ninhydrin reagent which is basically yellow in color, but when reacted with the amino acids, the resultant product is in purple colour which indicates that amino acid is present in that very compound.Bluish violet is correct, ref ptb part 2 chem pg 262 (Ninhydrin Test).

Question 16

Reaction of CH3CH2MgBr with ethylene epoxide gives:

Accepted Answer

B. 1 - butanol — The reaction of CH3CH2MgBr (ethylmagnesium bromide) with ethylene oxide (ethylene epoxide) typically results in the formation of 1,2-propanediol. This reaction is an example of a nucleophilic substitution reaction in which the nucleophilic carbon of the organometallic reagent attacks the electrophilic carbon of the epoxide, leading to the formation of an alcohol.The reaction can be represented by the following equation:CH3CH2MgBr + C2H4O-> CH3CH2CH2OHIn this reaction, the ethylmagnesium bromide acts as a nucleophile, attacking the epoxide ring and displacing the bromide ion. The resulting intermediate is an alkoxide ion, which quickly protonates to form the corresponding alcohol, 1,2-propanediol.It's important to note that the reaction conditions, such as temperature, solvent, and presence of any catalysts, can influence the outcome of the reaction. However, under typical conditions, the reaction described above is the most common result.Ethylene epoxide reacts with Grignard’s Reagent to produce an additive product, which upon hydrolysis yields a primary alcohol. The type of primary alcohol depends upon the number of C atoms in the grignard reagent’s ‘R’ group (RMgX).Since we have two C in Grignard’s Reagent and two in ethylene epoxide, the total number of carbon atoms in primary alcohol will be four, so the name of the alcohol formed is 1-butanol.

Question 17

Which type of alkyl halides gives SN2 mechanism?

Accepted Answer

D. Primary alkyl halides — The SN2 (Substitution Nucleophilic Bimolecular) mechanism typically occurs with primary (1°) alkyl halides. The SN2 mechanism involves a nucleophilic attack by a nucleophile on the electrophilic carbon of the alkyl halide, resulting in the substitution of the halogen atom with the nucleophile. In the SN2 reaction, the nucleophile approaches the carbon atom from the opposite side of the leaving group, leading to inversion of stereochemistry.The SN2 mechanism is favored for primary alkyl halides because the carbon atom attached to the halogen is less sterically hindered compared to secondary or tertiary carbon atoms. The steric hindrance created by bulky groups attached to the carbon atom can hinder the approach of the nucleophile and decrease the likelihood of an SN2 reaction.For example, an SN2 reaction can occur with a primary alkyl halide such as methyl chloride (CH3Cl):CH3Cl + Nu^- -> CH3Nu + Cl^-In this reaction, Nu^- represents the nucleophile, which can be an anionic species such as hydroxide ion (OH^-) or cyanide ion (CN^-).It's important to note that there are other mechanisms, such as SN1 (Substitution Nucleophilic Unimolecular) and E1 (Elimination Unimolecular), which occur with different types of alkyl halides depending on their structure and reaction conditions.SN2 reactions, or Bimolecular Nucleophilic Substitution reactions involve two molecules, the nucleophile and the alkyl halide in the slow step of the process. The mechanism involves an attack from the nucleophile and simultaneous removal of the leaving group from the alkyl halide molecule. This happens for primary alkyl halides only because they have the least steric hindrance (as compared to tertiary or secondary alkyl halides) to allow the attack from nucleophiles. Therefore, option D is correct.

Question 18

Pick correct pair about the difference between E1 and E2 mechanism of tertiary butyl bromide forming an alkene.

Accepted Answer

B. E1 mechanism- weak base and alkyl halide, E2 mechanism- strong base and alkyl halide — E1 mechanism- weak base and alkyl halide, E2 mechanism- strong base and alkyl halide.In the E1 mechanism, the rate-determining step is the formation of a carbocation intermediate, followed by the loss of a leaving group and the formation of a double bond. The reaction proceeds in two steps and requires a strong base to remove a proton from the beta-carbon.In contrast, in the E2 mechanism, the reaction occurs in a single step and requires a strong base to remove a proton from the beta-carbon and eliminate the leaving group at the same time.so, in this case both E1 and E2 mechanisms can occur. However, the E1 mechanism is favored with a weak base, whereas the E2 mechanism is favored with a strong base. Therefore, the correct pair is B) El mechanism- weak base and alkyl halide, E2 mechanism- strong base and alkyl halide.

Question 19

Alkyl halides can also be obtained by halogenation of _.

Accepted Answer

C. Alkanes — The reaction of a halogen with an alkane in the presence of ultraviolet (UV) light or heat leads to the formation of a haloalkane (alkyl halide). An example is the chlorination of methane. Experiments have shown that when the alkane and halogen reactants are not exposed to UV light or heat, the reaction does not occur.

Sindh Mdcat Exclusive Course Chemistry Alkyl Halides And Amines — Solved Past Paper with Answers

More Sindh / DUHS Solved Papers