Test: Stereochemistry Level - 1


20 Questions MCQ Test Organic Chemistry | Test: Stereochemistry Level - 1


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QUESTION: 1

Which one of the following statement is true?

Solution:

Diastereomers have different physical properties. They can be separated by ordinary separation techniques such as fractional crystallization.

QUESTION: 2

On Pluto, where everything is frozen, astronauts discovered two forms of 1, 2-dibromoethane; gauche and anti. Assuming that there are no rotations around single bonds, which statement about the two forms is correct:

Solution:

Gauche and anti-conformers are stereoisomers not related by mirror-image relationship, hence diastereomers.

QUESTION: 3

Which type of conformation is shown by I and II?

Solution:
QUESTION: 4

The most stable conformation of ethylene glycol is ______.

Solution:
  • Fully eclipsed conformation: the rotation of the gauge conformation to 60 degrees results in the gauge conformation and it is the least stable conformation of all.
  • Hence, the most stable conformation of ethylene glycol is gauche conformation.
QUESTION: 5

In the boat conformation of cyclohexane, the most destabilizing interaction is:

Solution:
  • Eclipsed atoms are not valid in boat configurations.

  • Flagpole interaction generally raises the strain and then energy in cyclohexane (boat conformational structure).
  • You can imagine this as two hydrogen atoms at pole position (1, 4) and the interaction between them.
  • The boat conformations have higher energy than the chair conformations. The interaction between the two flagpole hydrogen atoms, in particular, generates steric strain.
  • Torsional strain also exists between the C2–C3 and C5–C6 bonds, which are eclipsed. Because of this strain, the boat configuration is unstable (i.e. is not a local energy minimum).

Hence D is correct.

QUESTION: 6

The reaction in which stereochemically different molecules react differently is called:

Solution:
  • The reaction in which stereochemically different molecules react differently is called stereospecific reaction.
  • Stereospecificity is the property of a reaction mechanism that lead to different stereoisomeric reaction products from different stereoisomeric reactants, or which operates on only one of the stereoisomers.
QUESTION: 7

The configurations at the two stereocentres in the compound given below are:

Solution:
QUESTION: 8

The configuration at the two stereocentres in the compound given below are:

Solution:
QUESTION: 9

The two compounds given below are:

Solution:
QUESTION: 10

In the following Markonikov addition reaction, the products A and B are:

Solution:
QUESTION: 11

Epoxidation of (R)-cyclohexene-2-ol with peracetic acid yields a 95:5 mixture of compounds A and B compounds A and B are:

Solution:
QUESTION: 12

Among the following the most stable isomer for 3-methoxycylohexanol is:

Solution:
  • There is a possibility of Hydrogen Bonding between "Hydrogen(H)" of OH group and "Oxygen(O)" of OMe group. 
  • So if they are oriented in such a way that these two groups are close to each other , the strength of hydrogen bond would increase making it more stronger.
  • Hence, Option A, because of Hydrogen Bonding becomes the most stable isomer. 
QUESTION: 13

What is the relation between shown compounds?

Solution:
QUESTION: 14

Which of the following term best describes the pair of compounds shown?

Solution:
QUESTION: 15

The first person to separate a racemic mixture into individual enantiomers is:

Solution:

Louis Pasteur was the first documented person to separate stereoisomers.

QUESTION: 16

Among the following dibromocyclohexanes, the one that reacts fastest with sodium iodide to give cyclohexene is:

Solution:
  • The above reaction is an example of E2 elimination.
  • For E2 elimination both the leaving group must be anti w.r.t each other in the adjacent carbon atoms.
  • In option C, we get this requirement of anti geometry of the Br atoms, so it undergoes reaction. 
     
QUESTION: 17

Which of the following term best describes the pair of compounds shown?

Solution:
QUESTION: 18

Which structure is different from the following?

Solution:

The two substituents in the cis 1,4-disubstituted chair cyclohexane shown are necessarily axial and equatorial, as in (a), (b) and (d). In (c), however, the 1,4-substituents are both equatorial so this is the trans isomer, i.e. a different compound.

QUESTION: 19

The correct order of stability for the following conformations of cyclohexane is:



Solution:
QUESTION: 20

Which of the following statements can be deduced about the stereochemistry of this compound?

organic-chemistry-questions-answers-stereochemistry-q10

Solution:

In identifying stereogenic centers, any quaternary or tertiary carbons would be a good place to look. There are no quaternary carbons, and all the tertiary carbons are part of a benzene ring structure.

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