Question

If one hydrogen in a hydrocarbon is replaced by a halogen atom, the number of isomers that exist for the substituted compound depends on the number of types of hydrogen in the original hydrocarbon. Thus there is only one form of chloroethane (all hydrogens in ethane are equivalent), but there are two isomers of propane that arise from the substitution of a methyl hydrogen or a methylene hydrogen. How many isomers can be obtained when one hydrogen in each of the compounds named below is replaced by a chlorine atom? a. \(n\) -pentane c. 2,4 -dimethylpentane b. 2 -methylbutane d. methylcyclobutane

Short answer

The number of isomers for each compound obtained when one hydrogen is replaced by a chlorine atom are as follows: a. n-pentane: 2 isomers (1-chloropentane, 2-chloropentane) b. 2-methylbutane: 3 isomers (1-chloro-2-methylbutane, 2-chloro-2-methylbutane, 3-chloro-2-methylbutane) c. 2,4-dimethylpentane: 2 isomers (1-chloro-2,4-dimethylpentane, 3-chloro-2,4-dimethylpentane) d. methylcyclobutane: 2 isomers (chloromethylcyclobutane, 1-chloroethylcyclobutane)

Step-by-step solution

Identify the types of hydrogens in n-pentane

n-pentane has the structure CH3(CH2)3CH3, we have 3 types of hydrogens: 1. Terminal hydrogens on two CH3 groups (total 6 hydrogens) 2. Internal hydrogens on three CH2 groups (total 6 hydrogens)

Replace one hydrogen atom with a chlorine atom

Since we have 2 types of hydrogens, we can form two isomers: 1. Replace one terminal hydrogen: 1-chloropentane 2. Replace one internal hydrogen: 2-chloropentane Thus, there are 2 isomers for n-pentane when a hydrogen is replaced by a chlorine atom. #b. 2-methylbutane#

Identify the types of hydrogens in 2-methylbutane

2-methylbutane has the structure (CH3)2CHCH2CH3, we have 3 types of hydrogens: 1. Terminal hydrogens on three CH3 groups (total 9 hydrogens) 2. Internal hydrogens on one CH2 group (total 2 hydrogens) 3. Internal hydrogen on the CH group (total 1 hydrogen)

Replace one hydrogen atom with a chlorine atom

Since we have 3 types of hydrogens, we can form three isomers: 1. Replace one terminal hydrogen: 1-chloro-2-methylbutane 2. Replace one internal hydrogen on CH2: 2-chloro-2-methylbutane 3. Replace the internal hydrogen on CH: 3-chloro-2-methylbutane Thus, there are 3 isomers for 2-methylbutane when a hydrogen is replaced by a chlorine atom. #c. 2,4-dimethylpentane#

Identify the types of hydrogens in 2,4-dimethylpentane

2,4-dimethylpentane has the structure (CH3)2CH(CH2)2CH(CH3)2, we have 2 types of hydrogens: 1. Terminal hydrogens on four CH3 groups (total 12 hydrogens) 2. Internal hydrogens on two CH2 groups (total 4 hydrogens)

Replace one hydrogen atom with a chlorine atom

Since we have 2 types of hydrogens, we can form two isomers: 1. Replace one terminal hydrogen: 1-chloro-2,4-dimethylpentane 2. Replace one internal hydrogen: 3-chloro-2,4-dimethylpentane Thus, there are 2 isomers for 2,4-dimethylpentane when a hydrogen is replaced by a chlorine atom. #d. methylcyclobutane#

Identify the types of hydrogens in methylcyclobutane

methylcyclobutane has the structure CH3C3H6, with the methyl group attached to a cyclobutane ring. We have two types of hydrogens in this molecule: 1. Terminal hydrogens on the CH3 group (total 3 hydrogens) 2. Internal hydrogens on the cyclobutane ring (total 6 hydrogens)

Replace one hydrogen atom with a chlorine atom

Since we have 2 types of hydrogens, we can form two isomers: 1. Replace one terminal hydrogen: chloromethylcyclobutane 2. Replace one internal hydrogen: 1-chloroethylcyclobutane Thus, there are 2 isomers for methylcyclobutane when a hydrogen is replaced by a chlorine atom.

Key concepts

Halogen Substitution

Halogen substitution is a fundamental reaction in organic chemistry where a hydrogen atom in a hydrocarbon is replaced by a halogen atom, such as chlorine or bromine. This process significantly alters the properties of the molecule, leading to the formation of different isomers. Isomers are compounds with the same molecular formula but different structures, and thus different chemical properties.
When conducting halogen substitution, the type and position of hydrogen atoms in the original hydrocarbon determine the possible isomers. For instance, in the case of alkanes, replacing a hydrogen atom can occur at different locations on the carbon chain, leading to structural isomers.

• This reaction type is used extensively in producing alkyl halides and in the modification of organic molecules.
• It allows for the synthesis of specific chemical properties by simple variation of the carbon backbone's halogen-substituted points.
• Understanding these reactions is crucial for further functional group interconversions in organic synthesis.

Overall, halogen substitution is a versatile technique in organic synthesis for the creation of complex molecules from simple hydrocarbons.

Hydrogen Types

In organic molecules, hydrogen atoms can be classified based on their position, which influences their reactivity and role in halogen substitution. Recognizing these distinctions is key in predicting the number of possible isomers in a halogenated compound.
1. **Terminal Hydrogens** occur in methyl groups (CH₃) at the end of a carbon chain. These are often the most accessible and frequently substituted in reactions.
2. **Secondary or Internal Hydrogens** are found in methylene (CH₂) groups located within a carbon chain. These hydrogens require more energy for substitution due to greater steric hindrance and less accessibility.
3. **Tertiary Hydrogens** are attached to a carbon atom that is connected to three other carbon atoms. These are often more reactive in certain contexts due to the increased stability of the resulting carbocation intermediate.

• Understanding these hydrogen types helps chemists predict reactivity patterns during halogen substitution.
• Each type of hydrogen substitution leads to different structural isomers, affecting the final chemical properties of the compound formed.

Chloroalkanes

Chloroalkanes, also known as alkyl chlorides, are organic compounds wherein one or more hydrogen atoms have been replaced by chlorine. This substitution endows the molecule with unique physical and chemical properties that are distinct from the parent hydrocarbon.
These compounds serve as vital intermediates in organic synthesis and industrial applications. They exhibit increased density and lower boiling points compared to their hydrocarbon counterparts, allowing for easier manipulation in various chemical processes.

• Chloroalkanes are often used in the production of solvents, plastic products, and as intermediates in pharmaceuticals.
• They exhibit good solubility in organic solvents, making them useful in multiple extraction and purification techniques.
• Due to the presence of the chloro group, chloroalkanes demonstrate increased reactivity, allowing for further functionalization in the synthesis of more complex molecules.

Recognizing the formation and isomerization of chloroalkanes is crucial in the understanding of substitution reactions in organic chemistry.

Organic Chemistry

Organic chemistry is the branch of chemistry that focuses on the structure, properties, composition, reactions, and synthesis of carbon-containing compounds. These compounds include hydrocarbons and their various derivatives. It is essentially the study of life and all of the chemical reactions related to life.
Organic chemistry is vast, encompassing everything from small molecules to large polymers and biomolecules. The discipline's core lies in understanding how carbon's unique ability to form stable bonds leads to the diversity of organic compounds.

• Organic reactions often involve transformations that convert one type of organic compound into another, such as halogen substitution.
• The understanding of organic mechanisms provides insight into reaction products, enabling chemists to predict outcomes and to design new synthetic routes.
• Organic chemistry is essential in pharmaceuticals, agriculture, petrochemicals, and materials science due to its application in creating molecules that affect health, energy, and materials.

The principles of organic chemistry are crucial for exploring and harnessing new materials and chemicals to respond to global challenges.