Hydroxy Functional Group - Alcohols | Organic Chemistry 1

The hydroxy functional group (alcohol) is studied in this chapter: naming and properties of alcohols, synthesis of alcohols (SN reaction, reduction of carbonyls, organometallics), carbon-carbon bonds formation

Properties of Alcohols

Alcohols exhibit molecular polarity due to the electronegativity of oxygen ⇒ alcohols are soluble in water and polar solvents

 

Hydroxy functional group forms hydrogen bonds with other alcohol molecules ⇒ alcohols have a high boiling point compared to the corresponding alkanes

 

Alcohols are amphoteric: they can be deprotonated by strong bases or protonated by strong acids

Naming the Alcohols

1) Find the longest chain containing the OH
2) Number the chain starting with the end closest to the OH (if equal, start with the end closest to the first substituent)
3) Write the number corresponding to the OH position before the parent name. Use the suffixes diol, triol ... if there is more than one OH. For cyclic alcohols, carbon number 1 is the carbon bearing OH (it does not need to be mentioned if there is only one substituent)
4) Add the positions and names of the substituents as prefixes
 

Synthesis of Alcohols by SN Reactions

Alcohols can be synthesized by SN reactions. However, these synthetic conditions also lead to the formation of alkenes by E reactions
 


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To avoid competition between SN and E reactions, the halogen atom can be replaced by a better leaving group
 

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Synthesis of Alcohols by Reduction of Carbonyls

Carbonyl groups:  

Functional group composed of a C=O bond

​​​​Because oxygen is more electronegative than carbon, it will be electron-rich and will react as a nucleophile. On the contrary the carbon is electrophilic
Carbonyls are formed by oxidation of alcohols using Na2Cr2O7 or PCC

 

Reduction of carbonyls:

Alcohols can be synthesized by reduction of carbonyls using H- donors (NaBH4 or LiAlH4) ⇒ H- is electron-rich and will react with the electrophilic carbon of a carbonyl. Then quenching with water will lead to the formation of the hydroxy function

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​​​Oxydation and reduction of alcohols:

Primary alcohol:

Secondary alcohol:


NB: LiAlH4 and NaBH4 are both capable of reducing aldehydes and ketones to the corresponding alcohol. However, LiAlH4 is by far the more reactive of the 2 compounds ⇒ NaBH4 is generally preferred for the oxydation of primary alcohol to avoid any degradation of the compound

Synthesis of Alcohols with Organometallics

Organometallics:

Chemical compounds containing at least one chemical bond between a carbon and a metal
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3 common types of organometallics (with R = alkyl chain):

- alkyl lithium RLi (R-Li+)
- Grignard reagent RMgBr (R-BrMg+)
- Gilman reagent R2CuLi (R-RCu+Li)

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​​​​​​​Reduction of carbonyls with organometallics:​​​​​​​

Alcohols can be synthesized by reduction of carbonyls using organometallics (R- donors) ⇒ R- is electron-rich and will react with the electrophilic carbon of a carbonyl. Then quenching with water will lead to the formation of the hydroxy function

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Reactions of Organometallics R-M (M= Li, MgBr or RCuLi):

Synthesis of alcohol and Carbon-Carbon bond formation:


Carbon-Carbon coupling reactions (only with Gilman reagent):

R2-CuLi + CH3CH2Br → R-CH2CH3​​​​​​​ + R-CuLiBr

​​​​​​​Strong reaction with water:

R-M + HOH → R-H + MOH