Alkenes & Alkynes Nomenclature

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Questions and Answers

Which type of diene has the highest stability?

Conjugated dienes (correct)

Cumulated dienes

Isolated dienes

All dienes have equal stability

What factor contributes to the stability of an alkene?

Number of substituents on the double bond (correct)

Number of beta hydrogens

Number of alpha carbons

Presence of a hydroxyl group

Which of the following correctly describes Saytzeff's Rule?

Proton is removed from both beta and alpha carbons

Proton is removed from the most substituted carbon

Proton is removed from the least substituted carbon (correct)

Proton is removed from hydroxyl groups

What is the first step in the electrophilic addition reaction of alkenes?

Pi electrons attack the electrophile Signup and view all the answers

Alkenes can be synthesized from which of the following?

Alkyl halides and alcohols Signup and view all the answers

What are the products of dehydrohalogenation of an alkyl halide?

Alkene and HX Signup and view all the answers

The alpha hydrogen is defined as which of the following?

A hydrogen on the first carbon attached to a functional group Signup and view all the answers

Which of the following statements about carbocations is correct?

Carbocations readily react with nucleophiles Signup and view all the answers

What suffix is used in the IUPAC naming system to indicate the presence of a triple bond in hydrocarbons?

-yne Signup and view all the answers

How are compounds with two triple bonds named in the IUPAC system?

Diynes Signup and view all the answers

What is the common name for the simplest alkyne, H-C≡C-H?

Acetylene Signup and view all the answers

What type of reaction is primarily used to synthesize alkynes from dihalides?

E2 elimination Signup and view all the answers

During hydrohalogenation of alkynes, what product is initially formed after the first equivalent of HX is added?

Vinyl halide Signup and view all the answers

What is the fate of the enol produced during hydration of an alkyne in the presence of a strong acid and Hg2+ catalyst?

It converts to a carbonyl compound Signup and view all the answers

When numbering the carbon chain of a compound containing both double and triple bonds, what is emphasized in IUPAC nomenclature?

The first site of unsaturation Signup and view all the answers

What is the general trend in the addition reactions of alkynes due to the presence of weak π bonds?

They typically undergo multiple sequential additions Signup and view all the answers

What is the correct order of stability for carbocations from most stable to least stable?

3o > 2o > 1o > methyl Signup and view all the answers

What is the result of hydrating an alkene in the presence of concentrated sulfuric acid?

An alcohol Signup and view all the answers

In the addition of HX to an alkene, which carbon atom does the proton attach to according to Markovnikov's Rule?

The carbon with fewer substituents Signup and view all the answers

What is the main outcome of a halogenation reaction with alkenes?

Formation of a vicinal dihalide Signup and view all the answers

What type of product is formed when HBr is added in the absence of peroxide?

Markovnikov's product Signup and view all the answers

Which statement is true about alkynes?

Terminal alkynes have the triple bond at the end of the carbon chain. Signup and view all the answers

Which step correctly identifies the electrophile in the addition of HBr in absence of peroxide?

Proton Signup and view all the answers

What type of catalyst is commonly used in the hydrogenation of alkenes?

Platinum Signup and view all the answers

What product is formed when 1-ethylcyclopentene reacts with HCl?

2-chloro-1-ethylcyclopentane Signup and view all the answers

In the presence of peroxide, what type of product is formed during the addition of HBr?

Anti-Markovnikov's product Signup and view all the answers

What difference in hydrogen atoms can you expect when comparing alkenes and alkynes?

Alkynes have four fewer hydrogens than alkenes. Signup and view all the answers

Which process describes the addition of elements X and OH to an alkene?

Formation of Halohydrin Signup and view all the answers

Which statement correctly describes the fission of the HBr bond in the presence of peroxide?

Homolytic fission occurs Signup and view all the answers

What is the IUPAC name of the product formed from HBr and 2-methylbutene in presence of peroxide?

2-Bromo-3-methylbutane Signup and view all the answers

In the context of alkenes, what does Markovnikov's rule state?

The hydrogen will attach to the more substituted carbon. Signup and view all the answers

What type of bond hybridization is present in alkynes?

sp hybridization Signup and view all the answers

What is the general molecular formula for alkenes?

C_nH_{2n} Signup and view all the answers

How are substituents and functional groups prioritized when numbering the carbon chain in an alkene?

Hydroxyl groups take precedence over both double bonds and alkyl groups. Signup and view all the answers

When naming a cyclic alkene, what is specified about the double bond?

The double bond is numbered as 1 but the '1-' is omitted from the name. Signup and view all the answers

In the nomenclature of alkenes, what suffix is used to replace the '-ane' ending of alkanes?

-ene Signup and view all the answers

When numbering carbon atoms in a chain with a double bond, what is the primary goal?

To assign the double bond the lowest possible numbers. Signup and view all the answers

Which term describes hydrocarbons that contain at least one carbon-carbon double bond?

Alkenes Signup and view all the answers

What must be indicated when naming alkenes with more than one double bond?

Use the suffix '-diene' for two double bonds and '-triene' for three. Signup and view all the answers

Which of the following steps is NOT part of naming alkenes?

Changing the suffix '-ene' to '-ane' for naming. Signup and view all the answers

What type of bond is formed by the side-by-side overlap of two 2p orbitals in alkenes?

Pi (π) bond Signup and view all the answers

Which of the following correctly describes the geometry of a carbon-carbon double bond in alkenes?

Trigonal planar with a bond angle of 120° Signup and view all the answers

In which scenario would a cis isomer of an alkene be formed?

Both substituents on the double bond are on the same side Signup and view all the answers

Why is the cis isomer of an alkene generally less stable than the trans isomer?

It experiences steric interactions between substituents Signup and view all the answers

What does the E,Z designation system in alkene stereoisomerism rely on?

The ranking of substituent groups by atomic number Signup and view all the answers

What is the consequence of the lack of rotation around a carbon-carbon double bond in alkenes?

It locks the molecule in a specific conformation Signup and view all the answers

How would you correctly name the compound with the structure 2-Chloro-4-Methyl-3-hexene?

2-Chloro-4-Methyl-3-hexene Signup and view all the answers

Which of the following statements is true regarding alkenes?

They contain at least one carbon-carbon double bond Signup and view all the answers

Study Notes

Alkene & Alkyne

Alkenes are hydrocarbons containing a carbon-carbon double bond.
General molecular formula: C_nH_2n
Unsaturated hydrocarbons
Suffix for alkenes is "ene"

Alkene Nomenclature

Step 1: Identify the longest carbon chain containing the double bond and name the compound using the suffix "-ene" instead of "-ane".
Step 2: Number the carbon atoms in the chain to give the double bond the lowest possible numbers.
Step 3: Indicate the position of the double bond with a number.
Step 4: If there is more than one double bond, use "diene," "triene," etc. in the name. Add prefixes to name substituents and list alphabetically. Substituents with the lowest numbers on the chain take priority.
Step 5: Name any substituents and arrange them alphabetically.
Step 6: Write the full name of the alkene.

Special Nomenclature

Vinyl group: CH₂=CH-
Allyl group: CH₂=CHCH₂-
Vinyl carbons: RCH=CH-CH₂
Allyl carbons: RCH₂CH=CH-CH₂R

Electronic Structure of Alkenes

Sp² hybridized carbon atoms.
One sigma (σ) bond formed by linear overlap.
One pi (π) bond formed by side-by-side overlap of p orbitals.
All atoms on the double bond are in one plane.
Bond angle between atoms is 120°.

Cis-Trans Isomers of Alkenes

Alkenes can exhibit cis-trans isomerism.
Cis isomers have identical groups on the same side of the double bond.
Trans isomers have identical groups on opposite sides of the double bond.
The cis isomer is generally less stable due to steric interactions.

Naming Stereoisomerism of Alkenes by E,Z Designation

E/Z system uses sequence rules to rank substituents on each double-bond carbon.
Rank substituents based on atomic number.
E: higher-ranked substituents are on opposite sides.
Z: higher-ranked substituents are on the same side.

Cahn-Ingold-Prelog Rules (CIP System)

Rule 1: Higher atomic number outranks lower atomic number.
Rule 2: If a decision cannot be reached by the first atoms, move further out until difference is found.
Rule 3: Multiple-bonded atoms are equivalent to the same number of single-bonded atoms.
Apply the rules to determine E or Z configuration.

Alkene Stability

More substituted alkenes are more stable.
The more alpha-hydrogens, the more stable.
The stability of alkenes depends on the number of alkyl groups attached to the carbons forming the double bond.

Synthesis of Alkenes

Alkenes can be prepared from alkyl halides by elimination reactions (dehydrohalogenation) using alcoholic potassium hydroxide (KOH).
Alkenes can be prepared from alcohols by dehydration.
Alcoholic KOH and concentrated sulfuric acid are used in the process.

Saytzeff Rule

The most stable alkene product is formed in elimination reactions.
Proton is removed from the carbon atom with fewest hydrogens.

Alkene Reaction-Electrophilic Addition

Pi electrons attack the electrophile.
Nucleophile attacks the carbocation.
Electrophiles are poor in electrons, while nucleophiles are rich in electrons.
Carbocation stability order: Tertiary > Secondary > Primary > Methyl.

Electrophilic Addition

Hydrogen atom from electrophile HBr attaches to one carbon in the double bond.
Bromide anion attaches to the other carbon.

Markovnikov's Rule

In addition reactions of HX to an alkene, the H atom adds to the carbon with fewer alkyl substituents while X adds to the carbon with more alkyl substituents.
If the double bond carbons have the same degree of substitution, a mixture of addition products is formed.

Hydration

Addition of water to alkenes using concentrated sulfuric acid according to Markovnikov’s rule.
The product is an alcohol.

Halogenation

Addition of X₂ (Cl₂ or Br₂) to an alkene to form a vicinal dihalide.
The double bond breaks and X₂ adds to the carbons.

Formation of Halohydrins

Addition of a halogen (Cl₂ or Br₂) and water (H₂O) to an alkene, to form a halohydrin.
This reaction forms OH on one carbon and halogen on the other carbon of the double bond.

Addition of Hydrogen (Hydrogenation)

Transition metal catalysts (e.g., Pd/C, PtO₂) are used to add hydrogen to an alkene, reducing it to an alkane in the presence of a catalyst (called catalytic reduction or catalytic hydrogenation).

Incomplete Reduction(Conversion of Alkynes to Cis Alkenes)

Addition of Hydrogen using Lindlar catalyst produces a cis alkene.
Lindlar catalyst is heterogeneous catalyst consisting of palladium on calcium carbonate poisoned with lead acetate and quinoline.

Incomplete Reduction(Conversion of Alkynes to Trans Alkenes)

Addition of H₂using the sodium/lithium catalyst in presence of NH₃ produces a Trans alkene.

Alkynes

Hydrocarbons containing a carbon-carbon triple bond.
General molecular formula: C_nH_2n-2, Four less hydrogens than maximum possible.
Sp hybridized, linear geometry, bond angles of 180°.

Alkynes nomenclature

Alkynes are named similarly to alkenes, changing the suffix to "-yne".
Numbering the carbon chain gives the triple bond the lowest number.
Diynes, triynes, enynes are named using prefixes.

Alkynes Reactions

Addition reactions are characteristic (two sequential steps).
Addition of one equivalent of reagent forms an alkene
Addition of a second equivalent of reagent yield product with four new bonds.
Hydrohalogenation: Addition of HX, two moles of HX are added.
Halogenation: Addition of X₂, two halogen atoms add.
Hydration: Addition of H₂O, yields ketone product when using HgSO₄ catalyst.

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Description

Test your knowledge on the nomenclature of alkenes and alkynes. This quiz will cover the rules for naming these unsaturated hydrocarbons, including identifying carbon chains and positioning double bonds. Perfect for chemistry students wanting to strengthen their understanding of organic compounds.