Test: Organic Chemistry - Nomenclature and Isomerism (September 9) - NEET MCQ

The compounds with each doubly bonded carbon attached to two different groups (like Cab=Cab, Cab=Ccd) exhibit geometrical isomerism i.e., cis and trans forms. The geometrical isomerism arises due to restricted rotation of double bond.

However, even though there is restricted rotation for triple bond, alkynes do not exhibit geometrical isomerism, since the triply bonded carbons are attached to one group each only.

Vapor density = Molecular weight/2

As both the compounds have same molecular weights, both will have the same vapour density. Hence, gaseous density of both ethanol and dimethyl ether would be same under identical conditions of temperature and pressure. The rest of these three properties; Vapour pressure, boiling point and heat of vaporization will differ as ethanol has hydrogen bonding whereas ether does not.

To determine which of the statements are correct, let's analyze each statement one by one.

Step 1: Analyze Statement I
Statement I: A pair of positional isomers differs in the position of the same functional group.

- Explanation: Positional isomers are compounds that have the same molecular formula and the same functional group but differ in the position of that functional group within the molecule. For example, consider butanol:
- 1-butanol (C₄H₁₀O) has the hydroxyl (-OH) group on the first carbon.
- 2-butanol (C₄H₁₀O) has the hydroxyl (-OH) group on the second carbon.

Thus, this statement is correct.

Step 2: Analyze Statement II
Statement II: A pair of structural isomers have the same relative molar mass.

- Explanation: Structural isomers have the same molecular formula but differ in the connectivity of their atoms. Since they have the same number and types of atoms, their molar masses will be the same. For example, both butanol and isobutanol (C₄H₁₀O) have the same molar mass despite differing structures.

Thus, this statement is correct.

Step 3: Analyze Statement III
Statement III: A pair of functional group isomers belongs to different homologous series.

- Explanation: Functional group isomers are compounds that have the same molecular formula but different functional groups. For example, ethanol (C₂H₆O) and dimethyl ether (C₂H₆O) are functional group isomers. They belong to different functional groups but can belong to the same homologous series if they have similar structural features. Therefore, this statement is incorrect.

Structural isomers of alcohol C₅H₁₁OH are as follow:-

The correct answer is Option B.
 
 
CH₃−CH=CH−CH=CH−CH₃
          2,4-hexadiene
 
Three different geometrical isomers of cis-cis, trans-trans and sic-trans are possible.
 

However, there is no such arrangement in structure i, it won’t have any non polar structure.

There are 4 final products, they are as follow:-

2 products of the structure above due to presence of a chiral carbon.

1 product of structure above due to absence of Chiral Carbon.

1 product of structure above due to absence of Chiral Carbon.

Hence, Options A, B are correct.

The correct answer is option A & D
The given image is Self-Explanatory.
We know that following are the cases when a compound is Optically Inactive:
1. When it does not have a chiral Carbon Atom eg.: Methyl bromide
2. When it has a Plane or Axis of Symmetry eg.: Tartaric Acid (these compounds are called as Meso Compounds)
3. When it forms a Racemic Mixture eg.: Equimolar mixture of d-Lactic Acid and l-Lactic Acid.
The given compound in the question possesses an Axis of Symmetry (shown in the attached image). Hence, it is Optically Inactive.
 

Correct option is
A: It is optically inactive due to the plane of symmetry &

B: It is optically inactive due to the center of symmetry

The presence of any kind of symmetry makes the compound optically inactive.