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Organic Chemistry, tests for alkenes
-bromine water decolourises from…
Organic Chemistry
Alkenes
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Reactions with alkenes
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oxidation of alkenes!!!
-> with cold dil H+ manganate(VII)
forms a diol
-> with hot conc H+ manganate (VII) leads to spliting across the double bond and oxidising separately.
- h-c-h leads to co2 and h20
- ch3-c-h leads to carboxylic acid
- ch3-c-ch3 leads to ketone formation
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Alcohols
formation of alcohols
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reduction of carbonyl compounds
aldehyde -> primary alcohol
ketone -> secondary alcohol
conditions : reducing agent (nabh4/lialh4)
reduction of carboxylic acid
ch3cooh + 4[h] -> ch3ch2oh + h20
conditions : nabh4/lialh4
OR h2(g)/ni and heat
hydrolysis of an ester by heating with dilute acid/alkali
- with acid
ch3cooch2ch3 + h20 <-> ch3cooh + ch3ch2oh
- with alkali
ch3cooch2ch3 + naoh -> ch3coo-na+ + ch3ch2oh (ethanol)
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Carbonyl Compounds
Aldehydes
prepared by
oxidation of primary alcohols
primary alcohol + [O] -> aldehyde + h20
conditions : acidified cr2o7 2-/acidified kmno4
(as oxidising agents)
heat under reflux
the primary alcohol is heated gently with acidified pottasiium dichromate (vi) solution the mixture turns green as the orange dichromate ions (CrO7 2-) are reduced to green Cr3+ ions
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Ketones
prepared by
oxidation of secondary alcohols
conditions : pottasium dichromate (vi) acidified with h2so4
same reactions !!
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tests for alkenes
-bromine water decolourises from orange brown to colourless
-cold dilute potassium permanganate turns from purple to colourless
when oxidation occurs acidified pottasium dichromate (VI) turns from orange -> green
(tertiary alcohols cannot be oxidised!)
carbonyl compounds are identified with 2,4-DNPH (dinitrophenylhydrazine) forms a deep orange precipitate in the presence of a carbonyl compound
Fehlings reagent when warmed with an ALDEHYDE the cu2+ ions are reduced to cu+ ions. leading to the formation of a red precipitate of copper(i) oxide ORIGINALLY BLUE
Tollens reagent is also called ammoniacal silver nitrate solution, when warmed with an ALDEHYDE the ag+ ions are reduced to ag atoms leading to the formation of a silver mirror