Alkanols - Lecture notes 1 PDF

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Summary

Alkanols, ethers and aminesAlcohol (OH) group  When the OH group is attached to an alkane the molecule is an alkanol  Can exist as primary, secondary and tertiary  Name the longest chain  Physical properties related to both water and alkanes  C1-C3 alkanols are soluable  H bondingDiols and Tr...

Description

Alkanols, ethers and amines Alcohol       

(OH) group When the OH group is attached to an alkane the molecule is an alkanol Can exist as primary, secondary and tertiary Name the longest chain Physical properties related to both water and alkanes C1-C3 alkanols are soluable H bonding

Diols and Triols 1. Diols  1,2-Ethandiol or ethylene used in antifreeze  Accidental ingestion of this can led to death due to the conversion of alcohol dehydrogenase enzyme  Treatment by haemodialysis and ethanol as ethanol is the preferred substrate (by keeping the patient drunk all active sites will be inhibited by alcohol instead of the diol and therefore the toxic product cannot be formed) 2. Triols  Glycerol (1,2,3-Propanetriol)  Bi-product of soap and bio-diesel manufacture  Used as emollient (skin moisturiser)  Sweetener  Polymer and explosives production (nitroglycerine) Boiling Points  

Alkanols have relatively high boiling points as a result of H bonding due to the hydroxyl group However as you increase the chain length, the hydrocarbon chain (hydrophobic) increases and therefore solubility decreases

Chemical Properties of Alkanols 1. Acid    

Alkanol can act as an acid The longer the chain the weaker the acid Will react with alkali metals to release hydrogen gas and an anion (alkoxide) Alkoxides are strong bases, and are used in organic synthesis when strong bases are required in a non-aqueous solution 2Na+ -OH + H2

2H2O + 2Na 2CH3CH2OH + 2Na 2. Base 

(Formation of sodium hydroxide)

2Na+ -OCH2CH3 + H2

(Formation of sodium ethoxide)

In the presence of a strong acid it will accept an proton to form an oxonium ion

Oxidation of Alkanols 1. Primary Alcohol 2. Secondary Alcohol 3. Tertiary Alcohol

Aldehyde Ketone

Carboxylic acids

Nucleophilic Substitution     



Ethers

The protonation of alkanols leads to the formation of oxonium ions Secondary and tertiary oxonim ions leads lose water to form carbocation’s These carbocation’s undergo nucleophilic attack (SN1) or elimination Primary carbocation’s are unstable, therefore primary oxonmium ions do not lose water but are directly attacked by nucleophiles (SN2) If the nucleophile is a primary alcohol then an ether is generated. This is a condensation reaction. Two molecules combine by removing a small molecule (Intermolecular Dehydration) Common in biological processes

Naming Ethers   

Select the longest chain Change the –yl of the other hydrocarbon to –oxy to obtain the alkoxy group name Combine the two names

Properties of Ethers     

More polar than alkanes due to oxygen Much less polar than alcohols as there is no hydrogen attached to the oxygen Some hydrogen bonding between ethers and water No hydrogen bonding between ether molecules Are not very reactive and therefore are used as solvents in chemical reactions

Amines

Alkanal and Alkanones (Aldehydes and Kentones)

Carboyle Group

Physical Properties    

Differing negativities between C and O there is a big difference between the two double bonds Due to polarity and dipole-dipole interactions the boiling points are higher than corresponding hydrocarbons Smaller carbonyl compounds are soluable in water due to their dipole-dipole interactions and hydrogen bonding With increasing hydrocarbon chainlength the water solubility decreases

Tollens Reagent   

Is used to distinguish between aldehydes and ketones Aldehyde produces a silver precipitate (slver mirror) from a colourless solution Ketone undergoes no change during the reaction...