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Questions and Answers
What is the molecular formula for alkenes?
What is the molecular formula for alkenes?
What type of hybridization occurs in alkenes?
What type of hybridization occurs in alkenes?
How are the longest carbon chains identified in alkenes?
How are the longest carbon chains identified in alkenes?
What kind of bond formation occurs between the sp2-hybridized orbitals?
What kind of bond formation occurs between the sp2-hybridized orbitals?
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How are multiple double bonds numbered in an alkene's name?
How are multiple double bonds numbered in an alkene's name?
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Which of the following represents the correct nomenclature for 1-butene?
Which of the following represents the correct nomenclature for 1-butene?
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What is the angle between sp2 hybridized orbitals in alkenes?
What is the angle between sp2 hybridized orbitals in alkenes?
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What is the primary characteristic of a pi bond in alkenes?
What is the primary characteristic of a pi bond in alkenes?
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What reaction involves the removal of a water molecule from an alcohol?
What reaction involves the removal of a water molecule from an alcohol?
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Which of the following is a characteristic of alkynes?
Which of the following is a characteristic of alkynes?
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Which of the following best describes Markovnikov’s Rule?
Which of the following best describes Markovnikov’s Rule?
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What type of reaction is used for the reduction of alkynes?
What type of reaction is used for the reduction of alkynes?
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In the addition of nucleophiles to alkenes, which type of bond fission occurs?
In the addition of nucleophiles to alkenes, which type of bond fission occurs?
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What is the general feature of a symmetric alkene during addition reactions?
What is the general feature of a symmetric alkene during addition reactions?
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Which species can act as a nucleophile in reactions involving alkenes?
Which species can act as a nucleophile in reactions involving alkenes?
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What is the primary function of bases in dehydrohalogenation of alkyl halides?
What is the primary function of bases in dehydrohalogenation of alkyl halides?
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Study Notes
Unsaturated Hydrocarbons
-
Alkenes (Olefins):
- Straight-chain alkenes follow alkane nomenclature rules, but use the suffix "-ene".
- Unsaturated hydrocarbons with the formula CnH2n, same as cycloalkanes.
- Hybridization is sp2, resulting in a trigonal planar molecular geometry.
sp² Hybrid Orbitals
- One 2s orbital combines with two 2p orbitals to form three sp2 hybrid orbitals.
- The molecule has a trigonal planar geometry with bond angles of 120°.
C-C Double Bond (C=C)
- Formed by overlap of two sp² hybrid orbitals (sigma bond) and two p orbitals (pi bond).
sp² Orbitals
- Located in a plane with 120° angles.
- The remaining p orbital is perpendicular to the plane.
Nomenclature
- Find the longest carbon chain containing the double bond.
- Number the carbons so the double bond carbons have the lowest possible numbers.
- If more than one double bond, number all, from lowest to highest, separated by commas.
- Substituents are added as prefixes, using the lowest possible numbers and in alphabetical order.
Synthesis of Alkenes
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Dehydration of Alcohols:
- Uses heat and a dehydrating agent (acids like H2SO4, H3PO4 or alumina).
- Removes a water molecule from the alcohol.
Alkynes (Acetylenes)
- Unsaturated hydrocarbons with the formula CnH2n-2.
- Contain sp hybridized carbon atoms.
- Have a linear molecular geometry.
C-C Triple Bond (C≡C):
- Formed by σ bond (overlap of sp hybridized orbitals) and two π bonds (overlap of two sets of p orbitals).
- Linear molecular geometry.
IUPAC Nomenclature (Alkynes)
- Select the longest carbon chain containing the triple bond (functional group).
- Number the carbon chain so that the triple bond gets the lowest possible numbers.
- Locate and name substituents.
Synthesis of Alkynes
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Dehydrohalogenation of Dihalides:
- Use strong bases (e.g., alkoxides, amides) at high temperatures.
- Removes two HX molecules from a dihalide.
Reactions of Alkenes and Alkynes
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Addition Reactions:
- Hydrogenation: Reduction using H2 and a catalyst (e.g., Pd/C).
- Halogenation: Addition of halogen molecules (e.g., Br2).
- Hydrohalogenation: Addition of HX (e.g., HBr).
- Hydration: Addition of H2O.
- Oxidation (Ozonolysis): Oxidising the alkene to carbonyl groups.
Markovnikov's Rule
- In hydrohalogenation of alkenes, the halogen adds to the carbon with the fewer hydrogen atoms. This is due to the relative stability of carbocations.
Nucleophiles
- Electron donors, nucleus-loving reagents.
- Negatively charged species (anions) like OH-, CN-, RO-.
- Neutral molecules with lone pairs of electrons like R3N, H3N, H2O.
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