Alkenes and Their Nomenclature
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Alkenes and Their Nomenclature

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Questions and Answers

What is the general formula for alkenes?

CnH2n

What is the hybridization of carbon atoms in alkenes?

sp²

What is the bond angle in alkenes?

120°

What is the IUPAC name for the following alkene: CH3-CH2-CH=CH-CH2-CH3?

<p>2-hexene</p> Signup and view all the answers

What is the common name for the alkene: CH3-CH2-CH=CH2?

<p>1-butylene</p> Signup and view all the answers

What is the IUPAC name for the alkene: CH2=CH-CH3?

<p>propene</p> Signup and view all the answers

What is the IUPAC name for the alkene: CH3-CH=CH-CH2-CH2-CH3?

<p>3-hexene</p> Signup and view all the answers

What is the common name for the alkene: CH2=CH2?

<p>ethylene</p> Signup and view all the answers

What is the common name for the alkene: CH3-CH=CH-CH3?

<p>2-butylene</p> Signup and view all the answers

What is the common name for the alkene: CH3-CH2-C=CH2?

<p>isobutylene</p> Signup and view all the answers

What is the IUPAC name for the following alkene: CH3-CH2-CH2-C=CH2?

<p>2-methyl-1-butene</p> Signup and view all the answers

What is the general formula for alkanes?

<p>CnH2n+2</p> Signup and view all the answers

What is the IUPAC name for the alkyl group: CH3-CH=CH-CH2-

<p>2-butenyl</p> Signup and view all the answers

What is the IUPAC name for the alkyl group: CH2=CH-

<p>ethenyl</p> Signup and view all the answers

What is the common name for the alkyl group: CH2=CH-

<p>vinyl</p> Signup and view all the answers

What is the IUPAC name for the alkyl group: CH3-CH=CH-

<p>1-propenyl</p> Signup and view all the answers

What is the IUPAC name for the alkyl group: CH2-CH=CH2-

<p>2-propenyl</p> Signup and view all the answers

What is the common name for the alkyl group: CH2-CH=CH2-

<p>allyl</p> Signup and view all the answers

What is the general formula for alkynes?

<p>CnH2n-2</p> Signup and view all the answers

The addition of hydrogen to an alkyne in the presence of Lindlar's catalyst will produce a trans alkene.

<p>False</p> Signup and view all the answers

The addition of sodium metal in liquid ammonia to an alkyne will produce a cis alkene.

<p>False</p> Signup and view all the answers

The addition of hydrogen gas to an alkene will produce an alkane.

<p>True</p> Signup and view all the answers

Which of the following reagents can be used to prepare alkenes from alkynes?

<p>All of the above</p> Signup and view all the answers

What is the IUPAC name for the following alkene: CH3-CH=CH-CH2-CH2-CH2-CH3?

<p>3-octene</p> Signup and view all the answers

What is the common name for the alkene: CH3-CH=CH2?

<p>propylene</p> Signup and view all the answers

Which of the following is the most stable alkene?

<p>CH3-CH=CH-CH3</p> Signup and view all the answers

What is the general formula for a compound containing two double bonds?

<p>CnH2n-2</p> Signup and view all the answers

What is the IUPAC name for the following compound: CH2=CH-CH=CH2?

<p>1,3-butadiene</p> Signup and view all the answers

What is the IUPAC name for the following compound: CH3-CH=CH-CH=CH-CH3?

<p>2,4-hexadiene</p> Signup and view all the answers

What is the general formula for a compound containing three double bonds?

<p>CnH2n-4</p> Signup and view all the answers

What is the IUPAC name for the following compound: CH2=CH-CH=CH-CH=CH2?

<p>1,3,5-hexatriene</p> Signup and view all the answers

What is the name of the reaction that produces an alkene from an alkyl halide?

<p>Dehydrohalogenation</p> Signup and view all the answers

What is the name of the reaction that produces an alkene from an alcohol?

<p>Dehydration</p> Signup and view all the answers

Which of the following is the most reactive alkyl halide?

<p>Tertiary alkyl halide</p> Signup and view all the answers

The order of reactivity of halogens in dehydrohalogenation is F > Cl > Br > I.

<p>False</p> Signup and view all the answers

The major product formed in dehydrohalogenation is always the more substituted alkene.

<p>True</p> Signup and view all the answers

The reaction of an alkene with bromine water (Br2/H2O) results in the formation of a vicinal dibromide.

<p>True</p> Signup and view all the answers

The reaction of an alkene with hydrogen bromide (HBr) is a Markovnikov addition reaction.

<p>True</p> Signup and view all the answers

The reaction of an alkene with potassium permanganate (KMnO4) is an oxidation reaction.

<p>True</p> Signup and view all the answers

The reaction of an alkene with ozone (O3) is an oxidative cleavage reaction.

<p>True</p> Signup and view all the answers

Study Notes

Alkenes

  • Alkenes are unsaturated hydrocarbons containing carbon-carbon double bonds.
  • Their general formula is CnH2n.
  • The carbon atoms in alkenes are sp2 hybridized.
  • The bond angle in alkenes is approximately 120°.

IUPAC Nomenclature of Alkenes

  • Select the longest continuous carbon chain containing the double bond.
  • Number the chain to give the double bond the lowest possible number.
  • Name the substituents and indicate their positions.
  • Replace the "-ane" suffix with "-ene".

Common/Trivial Names of Alkenes

  • Naming follows the corresponding alkane, replacing "-ane" with "-ylene."
    • Ethene → Ethylene
    • Propene → Propylene
    • Butene isomers → a- and β-butylene; isobutylene.

Unsaturated Alkyl Groups

  • Remove the "e" from the alkene name and add "-yl" to denote the group.
    • Vinyl
    • Allyl
    • 1-prop-yl

Unsaturated Hydrocarbons containing two or more double bonds

  • For compounds with two double bonds, the suffix is "-diene."
  • For compounds with three double bonds, the suffix is "-triene."
  • The longest chain containing the maximum number of double bonds is chosen.
  • The chain is numbered to give the double bonds the lowest possible numbers.

Preparation of Alkenes

  • By reduction of alkynes: Alkynes can be reduced to cis- and trans-alkenes using catalysts such as H2/Ni or H2/Pd-CaCO3 with syn addition leading to a cis alkene or Na / Li and NH3 with trans addition leading to the trans alkene
  • By elimination reactions:
    • From alkyl halides (dehydrohalogenation): Alcoholic KOH and heat eliminate HX from alkyl halides, forming alkenes. Saytzeff's rule predicts the more substituted alkene as the major product.
    • From dihalides (dehalogenation): A reaction with Zn/HAc removes X2 to form the alkene.
    • From alcohols (dehydration): Using conc. H2SO4 at 160 - 180°C, alcohols are dehydrated to form alkenes. The most substituted alkene is the major product.

Saytzeff's Rule

  • The major product of an elimination reaction is the alkene with the most alkyl substituents on the double-bonded carbon.
  • The order of reactivity for halogen elimination is Iodine > Bromine > Chlorine > Fluorine.
  • Tertiary alkyl halides are more reactive than secondary and primary alkyl halides.

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Description

This quiz covers key concepts about alkenes, including their structure, general formula, and hybridization. It also focuses on IUPAC nomenclature, common names, and unsaturated alkyl groups. Test your knowledge of unsaturated hydrocarbons and their properties.

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