Alkanes: Structure, Nomenclature, Isomerism MCQ Quiz - Objective Question with Answer for Alkanes: Structure, Nomenclature, Isomerism - Download Free PDF

CONCEPT:

Calculation of Stereoisomers

\(\text{Number of stereoisomers} = 2^n\)

• Stereoisomers are molecules that have the same molecular formula but differ in the spatial arrangement of atoms.
• The number of possible stereoisomers is determined using the formula:
• where n is the number of stereogenic centers (chiral centers and/or geometrical isomers).

EXPLANATION:

n (stereogenic unit) = 2, 22 = 4 stereoisomers are possible. 

• For 5-phenylpent-4-en-2-ol, we analyze the stereogenic units:
  • One chiral center at C2 (which has -OH, alkyl, and two other different groups).
  • One C=C double bond at C4=C5, which gives rise to cis-trans (E/Z) isomerism.
• Thus, the total number of stereogenic units is n = 2.
• Using the formula: 2² = 4 stereoisomers are possible.

Therefore, the correct answer is: 4 stereoisomers.

CONCEPT:

Cis-Trans Isomerism

• Cis-trans isomerism, also known as geometric isomerism, occurs in alkenes due to the restricted rotation around the carbon-carbon double bond.
• For a compound to exhibit cis-trans isomerism, each carbon atom of the double bond must have two different groups attached to it.

EXPLANATION:

• Analyzing each compound for cis-trans isomerism:
  • 1) (CH₃)₂C = CH - C₂H₅
    • One of the carbon atoms of the double bond has two identical groups (CH₃), so this compound does not show cis-trans isomerism.
    • 
  • 2) C₆H₅CH = CH - CH₃
    • Each carbon atom of the double bond has two different groups attached to it (C₆H₅ and H on one carbon, H and CH₃ on the other), so this compound can show cis-trans isomerism.
    • 
  • 3) CH₃CH = CClCH₃
    • Each carbon atom of the double bond has two different groups attached to it (CH₃ and H on one carbon, Cl and CH₃ on the other), so this compound can show cis-trans isomerism.
    • 
• Since both compound 2 and compound 3 can show cis-trans isomerism, the correct answer is option 4 (More than one of the above).

Therefore, the compounds that will show cis-trans isomerism are C₆H₅CH = CH - CH₃ and CH₃CH = CClCH₃.

Concept:

Isomers:

• These are compounds that have the same molecular formula but different structures or stereochemistries.
• There is a wide range of classification of organic molecules based on their structures.

Ring -Chain isomers:

• Ring chain isomerism is a type of structural isomerism.
• It is shown by compounds that are capable of forming stable ring compounds. The minimum number of carbons that must be present in order to show ring chain isomerism is three.
• The phenomenon of a compound existing in open-chain as well as ring form is called ring chain isomerism.
• Cyclic compounds formed by rings of 3,4,5,6 carbon atoms are called propane, butane, pentane hexane respectively.

Explanation:

• The formula of n-hexane is C₆H₁₄, it contains 6 carbon atoms.
• Hexane can form open chain as well as closed or cyclic compounds.
• There are 5 possible isomers of n-Hexane in Chain form which are formed by the different arrangement of carbon atoms along the chain.
• They are given below:

​

Hence, there are 5 chain isomers of n-Hexane.

• There are six cyclic isomers of n-Hexane. 

Additional Information

The number of isomers and the carbon atoms are given below:

Concept:

Isomers:

• These are compounds that have the same molecular formula but different structures or stereochemistries.
• There is a wide range of classification of organic molecules based on their structures.

Ring -Chain isomers:

• Ring chain isomerism is a type of structural isomerism.
• It is shown by compounds that are capable of forming stable ring compounds. The minimum number of carbons that must be present in order to show ring chain isomerism is three.
• The phenomenon of a compound existing in open-chain as well as ring form is called ring chain isomerism.
• Cyclic compounds formed by rings of 3,4,5,6 carbon atoms are called propane, butane, pentane hexane respectively.

Explanation:

• The formula of n-hexane is C₆H₁₄, it contains 6 carbon atoms.
• Hexane can form open chain as well as closed or cyclic compounds.
• There are 5 possible isomers of n-Hexane in Chain form which are formed by the different arrangement of carbon atoms along the chain.
• They are given below:

​

Hence, there are 5 chain isomers of n-Hexane.

• There are six cyclic isomers of n-Hexane. 

Additional Information

The number of isomers and the carbon atoms are given below:

Concept:

Isomers:

• These are compounds that have the same molecular formula but different structures or stereochemistries.
• There is a wide range of classification of organic molecules based on their structures.

Ring -Chain isomers:

• Ring chain isomerism is a type of structural isomerism.
• It is shown by compounds that are capable of forming stable ring compounds. The minimum number of carbons that must be present in order to show ring chain isomerism is three.
• The phenomenon of a compound existing in open-chain as well as ring form is called ring chain isomerism.
• Cyclic compounds formed by rings of 3,4,5,6 carbon atoms are called propane, butane, pentane hexane respectively.

Explanation:

• The formula of n-hexane is C₆H₁₄, it contains 6 carbon atoms.
• Hexane can form open chain as well as closed or cyclic compounds.
• There are 5 possible isomers of n-Hexane in Chain form which are formed by the different arrangement of carbon atoms along the chain.
• They are given below:

​

Hence, there are 5 chain isomers of n-Hexane.

• There are six cyclic isomers of n-Hexane. 

Additional Information

The number of isomers and the carbon atoms are given below:

Correct answer: 1 and 4) 

Concept:

• Rules for IUPAC Nomenclature:
  • Identify the longest continuous carbon chain and give it a name.
  • Identify and name the various entities that are linked to this chain.
  • Begin numbering the chain from the end that is closest to a substituent group.
  • Assign an appropriate number and name to each substituent group's position.
  • Assemble the name by naming the classes alphabetically by full name (e.g. cyclopropyl before isobutyl).
  • When alphabetizing, the prefixes di, tri, tetra, and others, which are used to label many classes of the same kind, are ignored.

Explanation:

• The given compound has the longest chain of ten carbon atoms and side chain is present on 5th carbon atom.
• Side chain of 5 carbon atoms is neo-Pentyl and in IUPAC system it is 2′,2′-Dimethyl propyl .
• Hence , the names of the compound are 
• (i) 5−(2′,2′-Dimethylpropyl)-decane

• (ii) 5-neo-Pentyldecane

Conclusion:

Thus, the correct IUPAC names of the given compound are 5 – (2′, 2′–Dimethylpropyl)-decane and 5 – neo-Pentyldecane respectively.

Additional Information

Correct answer: 3 and 4) 

Concept:

• Rules for IUPAC Nomenclature:
  • Identify the longest continuous carbon chain and give it a name.
  • Identify and name the various entities that are linked to this chain.
  • Begin numbering the chain from the end that is closest to a substituent group.
  • Assign an appropriate number and name to each substituent group's position.
  • Assemble the name by naming the classes alphabetically by full name (e.g. cyclopropyl before isobutyl).
  • When alphabetizing, the prefixes di, tri, tetra, and others, which are used to label many classes of the same kind, are ignored.

Explanation:

• The longest carbon chain is of 10 carbons along with one secondary butyl group present at the fifth carbon and one isopropyl groups present at the fourth carbon.
• Since the alkane has 10 carbon atoms, it is decane, viz., the longest chain.

Conclusion:

Thus,  the correct IUPAC names of the given compound are 5– sec-Butyl – 4– iso-propyldecane and  4–(1-methylethyl)– 5 – (1-methylpropyl)-decane

Additional Information

Concept:

Isomers:

• These are compounds that have the same molecular formula but different structures or stereochemistries.
• There is a wide range of classification of organic molecules based on their structures.

Ring -Chain isomers:

• Ring chain isomerism is a type of structural isomerism.
• It is shown by compounds that are capable of forming stable ring compounds. The minimum number of carbons that must be present in order to show ring chain isomerism is three.
• The phenomenon of a compound existing in open-chain as well as ring form is called ring chain isomerism.
• Cyclic compounds formed by rings of 3,4,5,6 carbon atoms are called propane, butane, pentane hexane respectively.

Explanation:

• The formula of n-hexane is C₆H₁₄, it contains 6 carbon atoms.
• Hexane can form open chain as well as closed or cyclic compounds.
• There are 5 possible isomers of n-Hexane in Chain form which are formed by the different arrangement of carbon atoms along the chain.
• They are given below:

​

Hence, there are 5 chain isomers of n-Hexane.

• There are six cyclic isomers of n-Hexane. 

Additional Information

The number of isomers and the carbon atoms are given below:

CONCEPT:

Calculation of Stereoisomers

\(\text{Number of stereoisomers} = 2^n\)

• Stereoisomers are molecules that have the same molecular formula but differ in the spatial arrangement of atoms.
• The number of possible stereoisomers is determined using the formula:
• where n is the number of stereogenic centers (chiral centers and/or geometrical isomers).

EXPLANATION:

n (stereogenic unit) = 2, 22 = 4 stereoisomers are possible. 

• For 5-phenylpent-4-en-2-ol, we analyze the stereogenic units:
  • One chiral center at C2 (which has -OH, alkyl, and two other different groups).
  • One C=C double bond at C4=C5, which gives rise to cis-trans (E/Z) isomerism.
• Thus, the total number of stereogenic units is n = 2.
• Using the formula: 2² = 4 stereoisomers are possible.

Therefore, the correct answer is: 4 stereoisomers.

Concept:

Isomers:

• These are compounds that have the same molecular formula but different structures or stereochemistries.
• There is a wide range of classification of organic molecules based on their structures.

Ring -Chain isomers:

• Ring chain isomerism is a type of structural isomerism.
• It is shown by compounds that are capable of forming stable ring compounds. The minimum number of carbons that must be present in order to show ring chain isomerism is three.
• The phenomenon of a compound existing in open-chain as well as ring form is called ring chain isomerism.
• Cyclic compounds formed by rings of 3,4,5,6 carbon atoms are called propane, butane, pentane hexane respectively.

Explanation:

• The formula of n-hexane is C₆H₁₄, it contains 6 carbon atoms.
• Hexane can form open chain as well as closed or cyclic compounds.
• There are 5 possible isomers of n-Hexane in Chain form which are formed by the different arrangement of carbon atoms along the chain.
• They are given below:

​

Hence, there are 5 chain isomers of n-Hexane.

• There are six cyclic isomers of n-Hexane. 

Additional Information

The number of isomers and the carbon atoms are given below:

CONCEPT:

Cis-Trans Isomerism

• Cis-trans isomerism, also known as geometric isomerism, occurs in alkenes due to the restricted rotation around the carbon-carbon double bond.
• For a compound to exhibit cis-trans isomerism, each carbon atom of the double bond must have two different groups attached to it.

EXPLANATION:

• Analyzing each compound for cis-trans isomerism:
  • 1) (CH₃)₂C = CH - C₂H₅
    • One of the carbon atoms of the double bond has two identical groups (CH₃), so this compound does not show cis-trans isomerism.
    • 
  • 2) C₆H₅CH = CH - CH₃
    • Each carbon atom of the double bond has two different groups attached to it (C₆H₅ and H on one carbon, H and CH₃ on the other), so this compound can show cis-trans isomerism.
    • 
  • 3) CH₃CH = CClCH₃
    • Each carbon atom of the double bond has two different groups attached to it (CH₃ and H on one carbon, Cl and CH₃ on the other), so this compound can show cis-trans isomerism.
    • 
• Since both compound 2 and compound 3 can show cis-trans isomerism, the correct answer is option 4 (More than one of the above).

Therefore, the compounds that will show cis-trans isomerism are C₆H₅CH = CH - CH₃ and CH₃CH = CClCH₃.

Concept:

Isomers:

• These are compounds that have the same molecular formula but different structures or stereochemistries.
• There is a wide range of classification of organic molecules based on their structures.

Ring -Chain isomers:

• Ring chain isomerism is a type of structural isomerism.
• It is shown by compounds that are capable of forming stable ring compounds. The minimum number of carbons that must be present in order to show ring chain isomerism is three.
• The phenomenon of a compound existing in open-chain as well as ring form is called ring chain isomerism.
• Cyclic compounds formed by rings of 3,4,5,6 carbon atoms are called propane, butane, pentane hexane respectively.

Explanation:

• The formula of n-hexane is C₆H₁₄, it contains 6 carbon atoms.
• Hexane can form open chain as well as closed or cyclic compounds.
• There are 5 possible isomers of n-Hexane in Chain form which are formed by the different arrangement of carbon atoms along the chain.
• They are given below:

​

Hence, there are 5 chain isomers of n-Hexane.

• There are six cyclic isomers of n-Hexane. 

Additional Information

The number of isomers and the carbon atoms are given below:

Correct answer: 1 and 4) 

Concept:

• Rules for IUPAC Nomenclature:
  • Identify the longest continuous carbon chain and give it a name.
  • Identify and name the various entities that are linked to this chain.
  • Begin numbering the chain from the end that is closest to a substituent group.
  • Assign an appropriate number and name to each substituent group's position.
  • Assemble the name by naming the classes alphabetically by full name (e.g. cyclopropyl before isobutyl).
  • When alphabetizing, the prefixes di, tri, tetra, and others, which are used to label many classes of the same kind, are ignored.

Explanation:

• The given compound has the longest chain of ten carbon atoms and side chain is present on 5th carbon atom.
• Side chain of 5 carbon atoms is neo-Pentyl and in IUPAC system it is 2′,2′-Dimethyl propyl .
• Hence , the names of the compound are 
• (i) 5−(2′,2′-Dimethylpropyl)-decane

• (ii) 5-neo-Pentyldecane

Conclusion:

Thus, the correct IUPAC names of the given compound are 5 – (2′, 2′–Dimethylpropyl)-decane and 5 – neo-Pentyldecane respectively.

Additional Information

Correct answer: 3 and 4) 

Concept:

• Rules for IUPAC Nomenclature:
  • Identify the longest continuous carbon chain and give it a name.
  • Identify and name the various entities that are linked to this chain.
  • Begin numbering the chain from the end that is closest to a substituent group.
  • Assign an appropriate number and name to each substituent group's position.
  • Assemble the name by naming the classes alphabetically by full name (e.g. cyclopropyl before isobutyl).
  • When alphabetizing, the prefixes di, tri, tetra, and others, which are used to label many classes of the same kind, are ignored.

Explanation:

• The longest carbon chain is of 10 carbons along with one secondary butyl group present at the fifth carbon and one isopropyl groups present at the fourth carbon.
• Since the alkane has 10 carbon atoms, it is decane, viz., the longest chain.

Conclusion:

Thus,  the correct IUPAC names of the given compound are 5– sec-Butyl – 4– iso-propyldecane and  4–(1-methylethyl)– 5 – (1-methylpropyl)-decane

Additional Information