Test: Isomerism (28 August) - JEE MCQ

C₆H₁₄ indicates saturated hydrocarbon i.e., an alkane. There are 5 chain isomers possible with this formula i.e., one linear, two monosubstituted, two distubstituted. Here are the isomers of C₆H₁₄ 

• When two or more compounds have the same molecular formula but the different position of functional groups are substituents, they are called positional isomers and the phenomenon is called position isomerism.
• Here 2-chloropropane and 1-chloropropane differ in position so they exhibit position isomerism.

2-Butene exist as cis and trans isomers. The cis-isomer has the two methyl groups on the same side and the trans-isomer has the two methyl groups on opposite sides.

Due to restricted rotation around double bond it exhibits geometrical isomerism.

• Tautomerism is a type of isomerism in which a molecule can exist in two different forms (tautomers) that are in equilibrium and can interconvert into each other by the migration of hydrogen atom or proton.
• In all three compounds, Hydrogen can migrate, and keto from can get converted into enol form. So, All three compounds I, II, and III can exhibit tautomerism.

Hence, the Correct Option is B

The isomer of ethanol(CH₃-CH₂-OH) is dimethyl ether(CH₃-O-CH₃). This is a functional isomer of ethanol.

Explanation:

• Functional isomers are the ones with the same molecular formula but different functional groups.
• The molecular formula for dimethyl ether is C2H6O similar to ethanol.
• Dimethyl ether has the structural formula CH3OCH3 and ethanol has the structural formula CH3CH2OH.
• Therefore, dimethyl ether is the functional isomer of ethanol as both have the same molecular formula but one is ether and the other is alcohol. 

Two molecules are described as stereoisomers if they are made of the same atoms connected in the same sequence, but the atoms are positioned differently in space.
Additional Information: Stereoisomers can be subdivided into: 
(i) Optical isomers: Optical isomers are those two compounds with the same chemical formula such that their mirror images are not superimposable on each other. Depending on the direction they rotate the plane of polarised light in a polarimeter, we have two forms of optical isomers. They are:

• Dextro Isomer: This rotates to right.
• Laevo Isomer: This rotates to left.

An example is butan-2-ol. It has four different groups attached to its second carbon atom.

(ii) Geometric isomers: In the case of disubstituted complexes, the substituted groups could either be adjacent or opposite to each other. This leads to geometric isomerism. Thus, we can prepare square planar complexes such as [Pt(NH₃)₄Cl₂]  in two forms, cis and trans. When the chlorine atoms are adjacent to each other, we get the cis form. When two chlorine atoms are opposite, we get the trans-form.

Meso forms of isomers are single compounds and their molecules are achiral hence they cannot be separated into pairs.

Additional Information: A meso compound or meso isomer is a non-optically active member of a set of stereoisomers, at least two of which are optically active. This means that despite containing two or more stereogenic centers, the molecule is not chiral. 

The aldehyde and ketone that can be represented by molecular formula C₃​H_6​O are propanal and propanone respectively.

Aldehyde - Propanal - CH_3​CH₂​CHO

Ketone - Propanone - CH₃​COCH_3​

These two carbon compounds are called functional isomers. They do not have the same physical properties since their functional group is different.

When hydrogen is present on one side of C=O group and other side is R, (RCHO), then it is an aldehyde group. When R is present on both sides of C=O group, then it is a ketone.

The specific rotation is given by the expression observed rotation/length X density, here as observed rotation is given as 3x and its length is given as x, while the density is 3/y, the specific rotation equals 3x/x(y/3) = y.

• The compounds acetaldehyde and ethenol exhibit tautomerism.
• Tautomerism is a special type of functional isomerism which arises in carbonyl compounds containing α-hydrogen atom, it is a change of keto form to enol form.