Alkynes
Alkynes Alkynes are molecules with a carbon-carbon triple bond due to the presence of 2 pi bonds and 1 sigma bond.
Due to the electron density located within this triple bond, alkynes are also able to act as nucleophiles. The more substituted an alkyne is, the more stable it is. Alkyne Nomenclature
Alkyne Acidity
Terminal alkynes are much stronger Bronsted acids than other hydrocarbons.
Differences in acidity strengths can be rationalised using the ARIO (Atom, Resonance, Induction, Orbitals) method. o Atom: What atom is the charge on? (Larger and more electronegative atoms stabilize the negative charge the greatest) o Resonance: the more resonance structures the more stable the molecule o Induction: electron withdrawing inductive effect (Stabilises the negative charge) & electron donating inductive effects (Destabilises the negative charge)
o Orbitals: the more s-character in the orbital, the more stable it is Preparation of Alkynes Alkynes can be prepared by the elimination (E2) of geminal or vicinal (alkyl) dihalides.
Usually, more than 2 equivalents of the base are used in order to shift the equilibrium toward the elimination products. When this happens, the terminal alkyne that is produced will be deprotonated to form the more stable anion. A proton source such as water is then used to protonate the alkynide anion.
Addition reactions of Alkynes These reactions are usually slow due to the high energy of the vinylic carbocation that is formed.
Reduction/Hydrogenation of Alkynes
Due to the electron density located within this triple bond, alkynes are also able to act as nucleophiles. The more substituted an alkyne is, the more stable it is. Alkyne Nomenclature
Alkyne Acidity
Terminal alkynes are much stronger Bronsted acids than other hydrocarbons.
Differences in acidity strengths can be rationalised using the ARIO (Atom, Resonance, Induction, Orbitals) method. o Atom: What atom is the charge on? (Larger and more electronegative atoms stabilize the negative charge the greatest) o Resonance: the more resonance structures the more stable the molecule o Induction: electron withdrawing inductive effect (Stabilises the negative charge) & electron donating inductive effects (Destabilises the negative charge)
o Orbitals: the more s-character in the orbital, the more stable it is Preparation of Alkynes Alkynes can be prepared by the elimination (E2) of geminal or vicinal (alkyl) dihalides.
Usually, more than 2 equivalents of the base are used in order to shift the equilibrium toward the elimination products. When this happens, the terminal alkyne that is produced will be deprotonated to form the more stable anion. A proton source such as water is then used to protonate the alkynide anion.
Addition reactions of Alkynes These reactions are usually slow due to the high energy of the vinylic carbocation that is formed.
Reduction/Hydrogenation of Alkynes
