alcohols and ethers

alcohols

  • All alcohols contain the hydroxy group (-OH) and have general form ROH

Nomenclature (naming):

IUPAC system: remove the “e” from the alkane parent group and replace with “ol” A number before the ”-ol” indicates position of OH group on parent carbon chain

Common Names: Use “alkyl” group + “alcohol”
Mixture: common & IUPAC names are merged sometimes

reactions

Reactions of the O-H bond

deprotonation (step 1)

Can break the bond between O-H bond

H atom (1 è) H+ proton (0 è) H- hydride (2 è)

How easy is it to lose the OH proton (deprotonation)?
We can look to the acidity of alcohols to answer this.

  • Lower pKa means more acidic proton, therefore equilibrium moves to the right.

  • This means an alcohol will not be deprotonated as easily as hydrochloric acid because the pKa of ROH is larger than pKa of HCl

forming an alkoxide

  • an alkoxide is formed - an alkoxide is the conjugate base (CB) of an ROH

  • CH3OH and H2O have similar pKa, Therefore, get a mixture of HO- (hydroxy) and H3CO- (methoxy) anions

  • NOT a good method for making alkoxides

    Creation of metal alkoxides using sodium or potassium metal

    Creation of metal alkoxides using sodium or potassium metal

  • Reactions go to completion (no equilibrium) with H2 gas bubbling out of solution.

  • Also, metal alkoxides are useful as bases in elimination reaction

Reactions of the O lone pairs

  • The oxygen of the alcohol has lone pairs of electrons

We now consider the reactions that can occur at the C-O bond of ROH Acid Conditions Needed

  • 2 things can happen; Sn or E

Reactions of the C-O bond

  • We now consider the reactions of the a-C-H bond of alcohols

Reactions of the a-C-H bond

ethers

  • Ethers are compounds in which an oxygen atom is bonded to two alkyl (or aryl) groups The two R groups can be the same (symmetrical ethers) or different (asymmetrical ethers)

Nomenclature (naming):

IUPAC system: ethers are named as substituted alkanes (“alkoxy”+”alkane”)(RO-R)

  • A number before the ”alkoxy” indicates position of OR group on parent carbon chain

  • Common Names: write “alkyl” groups in alphabetical order then add “ether” (R-O-R)Additional : historical names also apply

properties

  • Ethers are relatively inert compounds

  • Ethers are often used as solvents for organic reactions

Positive aspects of Ethers

  • Good solvents

  • Low boiling points (35 deg)

  • Not reactive

  • Does not mix with water (immiscible)

  • Excellent for extraction of organic material from water

Negative aspects of Ethers

  • Highly flammable

  • Forms explosive peroxides (RO-OR)