Alkenes and Hydrocarbon Nomenclature

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Questions and Answers

What characteristic differentiates alkenes from other hydrocarbons?

Presence of a carbon-carbon double bond (correct)

Absence of carbon-carbon bonds

Presence of a carbon-carbon single bond

Presence of a carbon-carbon triple bond

When naming alkenes, how should the chain of carbon atoms be numbered?

From either end of the chain without considering the double bond

Randomly to avoid confusion with substituents

So that double bond carbons have the lowest possible numbers (correct)

So that the carbon with the highest atomic number is the first

Which statement about the p bond in alkenes is true?

It has a lower energy barrier than a single bond

It can be easily broken by low amounts of energy

It limits rotation around the double bond (correct)

It allows for free rotation between bonded carbons

What prefix is used when naming cyclic alkenes?

Cyclo- Signup and view all the answers

What is the orientation of sp² orbitals in a double bond of an alkene?

120º relative to each other Signup and view all the answers

What is the general naming suffix for hydrocarbons that contain carbon-carbon triple bonds?

-yne Signup and view all the answers

In naming a compound with both double and triple bonds, which bond receives priority for lower numbering?

Double bonds always receive lower numbers than triple bonds. Signup and view all the answers

What occurs when a 1,2-dihaloalkane is treated with KOH or NaOH?

A two-fold elimination of HX occurs. Signup and view all the answers

How many types of compounds are named with the suffix '-yne'?

Any compound with at least one triple bond. Signup and view all the answers

What is the electronic structure of a carbon-carbon triple bond?

Formed by sp hybrid orbitals and unhybridized px and py orbitals. Signup and view all the answers

What determines whether an alkene is classified as cis or trans?

The arrangement of similar groups around the double bond Signup and view all the answers

In the context of alkene stability, which of the following statements is accurate?

Cis alkenes give off more heat during hydrogenation than trans alkenes Signup and view all the answers

Which designation indicates that the higher priority groups are on opposite sides of the double bond?

E Signup and view all the answers

According to the Cahn-Ingold-Prelog priority rules, how should atoms be ranked at a comparison point?

By the highest atomic number Signup and view all the answers

When considering stability, which order of alkene substitution is correct from most to least stable?

tetrasubstituted > trisubstituted > disubstituted > monosubstituted Signup and view all the answers

What does the term 'hyperconjugation' refer to in the context of alkene stability?

The stabilization due to the overlap of sigma bonds with empty p-orbitals Signup and view all the answers

Which of the following conditions is necessary for cis-trans isomerism to occur in alkenes?

Each carbon atom in the double bond must have two different substituents Signup and view all the answers

What does the 'Z' designation indicate in the context of alkene stereochemistry?

The two higher priority groups are on the same side Signup and view all the answers

What type of bond is present in acetylene (HCCH) which makes it shorter and stronger than single or double bonds?

Triple bond Signup and view all the answers

Which addition reaction of alkynes results in a tetrahalide product?

Initial addition with excess reagent Signup and view all the answers

What is the outcome of hydroboration-oxidation of terminal alkynes?

Formation of aldehydes Signup and view all the answers

How are alkynes reduced to form alkanes?

By adding two equivalents of H2 Signup and view all the answers

Which catalyst is used to obtain cis alkenes from alkynes?

Hydrogenated palladium on calcium carbonate Signup and view all the answers

What happens during the oxidative cleavage of internal alkynes?

Formation of two carboxylic acids Signup and view all the answers

Which reaction produces trans alkenes from alkynes?

Reduction with sodium or lithium in liquid ammonia Signup and view all the answers

What distinguishes a terminal alkyne from an internal alkyne?

Location of the triple bond at the end of a carbon chain Signup and view all the answers

Why is the keto form usually the only form observed in keto-enol tautomerism?

Due to lower energy stability compared to enol Signup and view all the answers

What is the pKa of terminal alkynes, indicating their acidity level?

Approximately 25 Signup and view all the answers

What is the primary requirement for the thermal cracking of alkenes?

Very high temperatures without a catalyst Signup and view all the answers

Which process is used for the dehydrohalogenation of alkyl halides?

Application of heat and KOH Signup and view all the answers

What occurs during the electrophilic addition of alkenes with HBr?

A carbocation and bromide ion are produced Signup and view all the answers

What does Markovnikov's rule state regarding the addition of HX to unsymmetrical alkenes?

H attaches to the more substituted carbon Signup and view all the answers

What is the major outcome when 2-methylpropene reacts with HCl?

One product predominates due to regioselectivity Signup and view all the answers

How do carbocations generally react in terms of stability?

Greater substitution increases carbocation stability Signup and view all the answers

What is the process of hydration of alkenes typically used for?

Addition of H2O to form an alcohol in acidic conditions Signup and view all the answers

What describes the structure of carbocations?

They are planar with a vacant p-orbital Signup and view all the answers

Which reagent is used for oxymercuration-demercuration in hydration of alkenes?

Mercuric acetate in THF Signup and view all the answers

What is the result of adding ozone to an alkene in ozonolysis?

Generation of ketones and/or aldehydes Signup and view all the answers

What is the main function of hydrogenation in the context of alkenes?

Addition of H2 across the double bond Signup and view all the answers

In oxidation reactions, how do alkenes react with potassium permanganate?

Cleavage to form carboxylic acids and carbon dioxide Signup and view all the answers

Which of the following describes the method of alkene oxidation through epoxidation?

Formation of a cyclic ether via addition of an oxygen atom Signup and view all the answers

Study Notes

Organic Chemistry: Alkenes and Alkynes

Alkenes: Hydrocarbons containing a carbon-carbon double bond.
Alkynes: Hydrocarbons containing a carbon-carbon triple bond.
Nomenclature: Alkenes and alkynes are named using IUPAC nomenclature, which prioritizes the location of the double or triple bond. Lower numbers are assigned to the carbons of the multiple bond.
Cis-Trans Isomers: Alkenes with different substituents on each carbon of the double bond can exist as cis (same side) or trans (opposite sides) isomers. Rotation about a double bond is restricted, unlike rotation around a single bond. This results in different geometric isomers.
E,Z Designation: For alkenes with more than two substituents on the double bond, E/Z isomerism is used.
Stability: The stability of alkenes depends on the number of alkyl substituents on the double bond. More substituted alkenes are more stable.
Synthesis: Alkenes and alkynes can be synthesized through various reactions, including elimination reactions. Elimination reactions involve removal of atoms or groups from adjacent carbon atoms to form a double or triple bond.
Reactions: Alkenes and alkynes participate in electrophilic addition reactions. Addition reactions are specific reactions that add atoms or functional groups across a carbon-carbon multiple bond (double or triple bond).
Markovnikov's Rule: During addition reactions to unsymmetrical alkenes, the hydrogen preferentially bonds to the carbon with the greater number of hydrogen or alkyl substituents. A higher substituted carbocation is preferred.
Hydration: Alkenes can be hydrated under specific conditions to yield alcohols.
Hydroboration-Oxidation: This method gives the anti-Markovnikov product during hydration of alkenes.
Reduction: Addition of H2 to alkenes or alkynes using catalysts such as Pd/C, Lindlar's catalyst, or alkali metals in liquid ammonia can result in alkanes or specific cis or trans isomers.
Oxidation: Ozonolysis and permanganate can cleave the multiple bond of alkenes, yielding carbonyl compounds.

Alkynes

Nomenclature: Alkynes use the suffix -yne. Numerical identifiers position the triple bond.
Acidity: Terminal alkynes react with strong bases to form acetylide anions. This is due to the high electronegativity of the triple bond.
Alkylation: Acetylide anions are strong enough nucleophiles and bases to directly react with primary halides to create longer alkyne chains.
Reactions: Addition reactions for alkynes follow similar principles to alkenes, producing stereoisomers.

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Description

This quiz explores the unique characteristics of alkenes compared to other hydrocarbons. Questions cover naming conventions, structural features, and the electronic properties of alkenes. Perfect for chemistry students looking to test their knowledge on this topic.