Podcast
Questions and Answers
What is the general formula for alkenes?
What is the general formula for alkenes?
What is the distinguishing feature of alkene structure?
What is the distinguishing feature of alkene structure?
Why are alkenes referred to as unsaturated hydrocarbons?
Why are alkenes referred to as unsaturated hydrocarbons?
What is the shortest member of the alkene family mentioned in the text?
What is the shortest member of the alkene family mentioned in the text?
Signup and view all the answers
How are most alkenes named according to IUPAC system?
How are most alkenes named according to IUPAC system?
Signup and view all the answers
In naming alkenes, how is the position of the double bond indicated?
In naming alkenes, how is the position of the double bond indicated?
Signup and view all the answers
What determines the position of the double bond in alkenes?
What determines the position of the double bond in alkenes?
Signup and view all the answers
Which solvent are alkenes quite soluble in?
Which solvent are alkenes quite soluble in?
Signup and view all the answers
What effect does increasing carbon number have on the boiling point of alkenes?
What effect does increasing carbon number have on the boiling point of alkenes?
Signup and view all the answers
What causes cis, trans isomerism in alkenes?
What causes cis, trans isomerism in alkenes?
Signup and view all the answers
In cis-2-butene, where are the two methyl groups located relative to the double bond?
In cis-2-butene, where are the two methyl groups located relative to the double bond?
Signup and view all the answers
Why can't cis-2-butene and trans-2-butene convert into each other at room temperature?
Why can't cis-2-butene and trans-2-butene convert into each other at room temperature?
Signup and view all the answers
Which process involves converting alkyl halides into alkenes by eliminating hydrogen halide?
Which process involves converting alkyl halides into alkenes by eliminating hydrogen halide?
Signup and view all the answers
When n-Butyl chloride undergoes dehydrohalogenation, which alkene is the major product?
When n-Butyl chloride undergoes dehydrohalogenation, which alkene is the major product?
Signup and view all the answers
How does sec-Butyl chloride differ from n-Butyl chloride in terms of dehydrohalogenation products?
How does sec-Butyl chloride differ from n-Butyl chloride in terms of dehydrohalogenation products?
Signup and view all the answers
What is the role of the hydroxide ion in dehydrohalogenation during alkyl halide conversion?
What is the role of the hydroxide ion in dehydrohalogenation during alkyl halide conversion?
Signup and view all the answers
How do alkenes usually form in a dehydrohalogenation reaction compared to free radical reactions?
How do alkenes usually form in a dehydrohalogenation reaction compared to free radical reactions?
Signup and view all the answers
What type of compounds are alcohols, based on their general formula ROH?
What type of compounds are alcohols, based on their general formula ROH?
Signup and view all the answers
Which species can accept a pair of electrons according to the text?
Which species can accept a pair of electrons according to the text?
Signup and view all the answers
What is the role of alumina in the dehydration process of alcohols?
What is the role of alumina in the dehydration process of alcohols?
Signup and view all the answers
In the dehydration mechanism, what is formed by the union of alcohol with a hydrogen ion?
In the dehydration mechanism, what is formed by the union of alcohol with a hydrogen ion?
Signup and view all the answers
What is lost in step 3 of alkene formation during dehydration?
What is lost in step 3 of alkene formation during dehydration?
Signup and view all the answers
From what species is the alkene formed in the dehydration process?
From what species is the alkene formed in the dehydration process?
Signup and view all the answers
Why is it stated that the alkene is not initially formed from the carbonium ion generated from alcohol?
Why is it stated that the alkene is not initially formed from the carbonium ion generated from alcohol?
Signup and view all the answers
What type of rearrangement can a carbonium ion undergo to form a more stable carbonium ion?
What type of rearrangement can a carbonium ion undergo to form a more stable carbonium ion?
Signup and view all the answers
Which type of cation can the 2-methyl-l-butyl cation rearrange into?
Which type of cation can the 2-methyl-l-butyl cation rearrange into?
Signup and view all the answers
What is the name for the migration of hydrogen with a pair of electrons?
What is the name for the migration of hydrogen with a pair of electrons?
Signup and view all the answers
In the synthesis of alkenes, what method involves the dehalogenation of vicinal dihalides?
In the synthesis of alkenes, what method involves the dehalogenation of vicinal dihalides?
Signup and view all the answers
What determines whether a cis-alkene or a trans-alkene predominates in the reduction of an alkyne to the double-bond stage?
What determines whether a cis-alkene or a trans-alkene predominates in the reduction of an alkyne to the double-bond stage?
Signup and view all the answers
Why is rearrangement necessary in the preparation of alkenes from carbonium ions?
Why is rearrangement necessary in the preparation of alkenes from carbonium ions?
Signup and view all the answers
A hydride shift involves the migration of an alkyl group with a pair of electrons.
A hydride shift involves the migration of an alkyl group with a pair of electrons.
Signup and view all the answers
The dehalogenation of vicinal dihalides is a common method for the synthesis of alkanes.
The dehalogenation of vicinal dihalides is a common method for the synthesis of alkanes.
Signup and view all the answers
Primary carbonium ions rearrange to form tertiary carbonium ions for increased stability.
Primary carbonium ions rearrange to form tertiary carbonium ions for increased stability.
Signup and view all the answers
The dehalogenation of vicinal dihalides involves compounds that have halogens on non-adjacent carbons.
The dehalogenation of vicinal dihalides involves compounds that have halogens on non-adjacent carbons.
Signup and view all the answers
The reduction of an alkyne to the double-bond stage can only yield a trans-alkene.
The reduction of an alkyne to the double-bond stage can only yield a trans-alkene.
Signup and view all the answers
A 2,3-dimethyl-2-butyl cation rearranges to form a 3,3-dimethyl-2-butyl cation.
A 2,3-dimethyl-2-butyl cation rearranges to form a 3,3-dimethyl-2-butyl cation.
Signup and view all the answers
The alkyl shift involves the migration of a hydrogen atom with a pair of electrons.
The alkyl shift involves the migration of a hydrogen atom with a pair of electrons.
Signup and view all the answers
In the preparation of alkenes, secondary carbonium ions rearrange to form primary carbonium ions for increased stability.
In the preparation of alkenes, secondary carbonium ions rearrange to form primary carbonium ions for increased stability.
Signup and view all the answers
Isomeric alkenes can be formed in the dehalogenation process of vicinal dihalides.
Isomeric alkenes can be formed in the dehalogenation process of vicinal dihalides.
Signup and view all the answers
The alkene formed in the reduction of an alkyne is determined solely by the position of the triple bond in the chain.
The alkene formed in the reduction of an alkyne is determined solely by the position of the triple bond in the chain.
Signup and view all the answers
Study Notes
Alkenes
- General formula: CnH2n
- Unsaturated hydrocarbons obtained from alkanes by loss of hydrogen in the cracking process
- Simplest member: ethylene (C2H4)
Structure of Alkenes
- Distinguishing feature: carbon-carbon double bond
- Double bond consists of a strong σ bond and a weak π bond
- C─C distance in ethylene is shorter than in ethane
Naming Alkenes
- IUPAC system used for naming
- Rules:
- Select the longest continuous chain containing the double bond as the parent structure
- Indicate the position of the double bond in the parent chain
- Carbon-carbon double bonds take precedence over alkyl groups and halogens in determining the main carbon chain and direction of numbering
Physical Properties
- Insoluble in water, but soluble in nonpolar solvents like benzene, ether, and chloroform
- Boiling point rises with increasing carbon number, similar to alkanes
Cis, Trans Isomerism in Alkenes
- Restricted rotation about the carbon-carbon double bond
- Example: 2-butene has two stereoisomers, cis-2-butene and trans-2-butene
- These compounds have different physical and chemical properties
Preparation of Alkenes
- Methods:
- Dehydrohalogenation of alkyl halides
- Dehydration of alcohols
- Dehalogenation of vicinal dihalides
- Reduction of alkynes
Dehydrohalogenation of Alkyl Halides
- Involves elimination of hydrogen halide
- Hydroxide ion pulls a hydrogen ion away from carbon, and a halide ion separates to form the double bond
Dehydration of Alcohols
- Requires presence of an acid and heat
- Can be carried out in two ways:
- Heating the alcohol with sulfuric or phosphoric acid
- Passing the alcohol vapor over alumina (A12O3), which acts as a Lewis acid
- Mechanism involves formation of a carbonium ion, which loses a hydrogen ion to form the alkene
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Learn about alkenes, unsaturated hydrocarbons obtained from alkanes by loss of hydrogen in the cracking process. Explore the general formula CnH2n and the distinguishing feature of carbon-carbon double bonds in the alkene structure.
