Chemistry - Reactions in Organic Chemistry Flashcards

reactions in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms

CH4 + Cl2 → CH3Cl + HCl
methane + chlorine → clorormethane + hydrogen cloride

C2H6 + CL2 → C2H5Cl + HCl
ethane + chlorine → chloroethane + Hydrogen chloride

Used as flame retardants

Free radical substitution mechanism

an atom or group of atoms with an unpaired electron which are highly reactive

homolytic fission is the splitting of a covalent bond where each atom takes one electron, forming free radicals

the presense of ultra- violet light

1. Initiation
   * Homolytic fission occours - A chlorine molecule is split into two chlorine free radicals in the presence of UV light

2. Propagation 1: A Chlorine free radical reacts with a methane molecule forming hydrogen chloride and a methyl free radical CH3

3. Propergation 2 : a methy free radical reacts with a separate chlorine molecule forming chloromethane and a chlorine free radical. This sets up a chain reaction until one reactant is used up. It causes constant formation of chloromethane and hydrogen chloride
   step 3: termination : The chain reaction ends when the free radicals combine to form chlorine, chloromethane and ethane

Uv light is required to cause homolytic fission and split Cl2 into Cl free radical

a) adding tetramethyl lead. It decomposes to form CH3 free radicals.
It causes an increase in rate of reaction, they promote the chain reaction.

b) for every photon of light absorbed, thousands of molecues of chloromethane are formed.

The formation of the hydrocarbon ethane in trace amounts must have come from the combination of CH3 radicals

the probability of CH3 radicals combining with other CH3 radicals is small due to the small concentration of CH3 radicals. There is a much higher probability of CH3 radicals combining eith Cl2 due to the large conc of Cl2

1. Initiation
   * Homolytic fission occours - A chlorine molecule is split into two chlorine free radicals in the presence of UV light

2. Propagation 1: A Chlorine free radical reacts with a ethane molecule forming hydrogen chloride and a ethyl free radical C2H5

3. Propergation 2 : a ethyl free radical reacts with a separate chlorine molecule forming chloroethane and a chlorine free radical. This sets up a chain reaction until one reactant is used up. It causes constant formation of chloroethane and hydrogen chloride
   step 3: termination : The chain reaction ends when the free radicals combine to form chlorine, chloroethane and butane

Uv light is required to cause homolytic fission and split Cl2 into Cl free radical

a) adding tetraethyl lead. It decomposes to form C2H5 free radicals.
It causes an increase in rate of reaction, the C2H5 radicals promote the chain reaction.

b) for every photon of light absorbed, thousands of molecues of chloroethane are formed.

The formation of the hydrocarbon butane in trace amounts must have come from the combination of C2H5 radicals

the probability of C2H5 radicals combining with other C2H5 radicals is small due to the small concentration of C2H5 radicals. There is a much higher probability of C2H5 radicals combining eith Cl2 due to the large conc of Cl2

An addition reaction is a chemical reaction in which two or more molecules react to form a single molecule

C2H4 + Cl2 → C2H4Cl2

C2H4 + Br2→ C2H4Br2

No, benzene is neither saturated nor unsaturated. Its bonds are an identical intermediate between a single and a double bond

C2H4 + HCl→ C2H4Cl

C2H4 + H2O→ C2H5OH

C2H4 + H2→ C2H6

Nickel.
Hydrogenation of vegtable oils produces soild fats used in ,margarines

the ionic addition mechanism - involves ions

the splitting of a covalent bond, where one atom takes BOTH electrons from the covalent bond forming a potive ion and a negative ion

the high electron density present in the alkene's double bond

1. Polaristaion.

• The Br2 molecule approaches the double bond of the ethene molecule

• It becomes polarised by the high electron density in the alkenes carbon- carbon double bond

1. Heterolytic fission

• The polarisation becomes so great that heterolytic fission occours and the Br2 molecule splits up into Br+ and Br- ions

1. Carbonium ion formation:

• The Br+ ion is attracted to the electrons in the electrons in the double bond and forms a sigma bond with the carbon, breaking the double bond

• Leaves the formation of an INTERMEDISTE carbonium ion
  4.Ionic addition:

• The intermediate carbonium ion is sttacked by the Br- ion, this results in the formation of 1,2-dibromoethane

1. Polaristaion.

• The Cl2 molecule approaches the double bond of the ethene molecule

• It becomes polarised by the high electron density in the alkenes carbon- carbon double bond

1. Heterolytic fission

• The polarisation becomes so great that heterolytic fission occours and the 2 molecule splits up into Cl+ and Cl- ions

1. Carbonium ion formation:

• The Cl+ ion is attracted to the electrons in the electrons in the double bond and forms a sigma bond with the carbon, breaking the double bond

• Leaves the formation of an INTERMEDIATE carbonium ion
  4.Ionic addition:

• The intermediate carbonium ion is sttacked by the Cl- ion, this results in the formation of 1,2-dichloroethane

1. Polaristaion.

• The Hδ+ in the polar HCl molecule approaches the double bond of the ethene molecule

• It becomes increasingly polarised by the high electron density in the alkenes carbon- carbon double bond

1. Heterolytic fission

• The polarisation becomes so great that heterolytic fission occours and the HCl molecule splits up into H+ and Cl- ions

1. Carbonium ion formation:

• The H+ ion is attracted to the electrons in the electrons in the double bond and forms a sigma bond with the carbon, breaking the double bond

• Leaves the formation of an INTERMEDISTE carbonium ion
  4.Ionic addition:

• The intermediate carbonium ion is sttacked by the Cl- ion, this results in the formation of chloroethane

This reaction can occour during the dark

(That a negative ion attacks a carbonium ion in step 4)
If only Bromine is added to ethene, the only product that can be formed is 1,2 dibromoethane.
However - If bromine water containing sodium chloride (Sources of Br-, OH-, and Cl-) are added to ethene, three separate products form

1,2-dibromoethane 2-bromoethanol 1-bromo2-chloroethane

These three different products suggest a postive intermediate carbonium ion is always formed that is subject to addition from different negative

A Chemical reaction in which a small molecule is removed from a larger molecule leaving a double bond in the larger molecule

C2H5OH -(Al2O3)→ H2O + C2H4
This is also called a dehydration reaction.

Al2O3

Bonds broken:Carbon to oxygen sigma bond broken,
Carbon to Hydrogen sigma bond broken.
Bonds Formed: Carbon to carbon Pi bonf
Oxygen to hydrogen sigma bonf

a subsution reaction.
Alkane uses chorine.
free radical mechanism

Addition reaction.
Alkene + Br2/Cl2/(H2 nickel catalyst.
Mechanism is Ionic addition

elimation reaction
(molecule with no double bonds)→(Alkene + chloroalkene)

A Primary Alcohol -(Oxidised)→ Aldehyde-(Oxidised)→Carboxylic acid

secondart alcohol -(oxidised)→ Ketone

Strong oxidising agents:Acidified sodium dichromate
Acidified potassium manganate(VII)
weak oxidising agents : Fehlings reagent
ammoniacal silver nitrate

Primary alcohol←Aldehyde ←Carboxylic acid

secondary alcohol ← Ketone

In the Presence of a hydrogen and a nickel catalyst

• the aldehyde is placed in a test tube in a warm water bath.

• using a dropper, acidified dilute potassium manganate VII is added to the aldehyde

• Result: the purple colour of the potassium manganate turns colourless

MnO4- + 8H+ +5e- → Mn2+ +4H20

MnO4- contain Mn7+ ions causing a purple colour.
when reacted with a colourless aldehyde in an acidic enviorment, Mn 7+ ions and reduced to Mn2+ ions. Mn2+ ions are colourless

Fehling's reagent is an equal mixture of fehling's A and Fehling's B
it is blue to the presence of copper Cu2+ ions

• the aldehyde is placed in a test tube in a warm water bath

• using a dropper, equal amounts of Fehlings A and Fehling's B are added to the aldehyde.

• result: The blue colour of fehling's reagent turns into a brick red precipitate

Cu2+ ---> Cu+↓
blue to a brick red perciptate

Fehling's solutio contains Cu2+ ions causing a blue colour
when reacted with an aldehyde the Cu2+ are reduced to Cu+ ions
Cu+ ions have a red colour and are not soluble so a brick red precipitate forms

Tollen's reagent
the colourlessness is caused by the Ag+ ions in the solution

If tollens reagent is stored, it is likely explosive products could form

• the aldehyde is placed in a test tube in a warm water bath.

• Using a dropper, ammoniacal silver nitrate is added to the aldehyde

• Result ; the colourless Ag+ solution reacts and a silver mirrir is formed on the inside of the test tube

Ethanal→ethanoic acid

Ag+ + 1e- → Ag↓

• Tollen's reagent contain Ag+ ion causes a colourless solution.

• when reacted with ethanal Ag+ ions are reduced to forn Ag.

• Ag precipitates out of solution causing a silver mirror.

propanone and butanone are ketones. Ketones ar very difficult to oxidise.
no reducation = no colour change

fehling's reagent or ammonical silver nitrate

a chemical reaction in which a larger molecule reacts with water causing it ro break up into smaller molecules

normal hydrolysis (w/ H2O)
Base hydrolysis (NaOH/KOH)

ester + Water → carboxylic acid + Alcohol

side goup of the ester
ester main chain

An ester is reacted with a base to form soap and achohol

Ester + Base → Soap + Alchohol

The ester side group bonds with the OH of the base
ester main chain bonds with the 'metal' of the base. (Na or K)

Methyl propanoate + NaOH → Methan-1-ol + sodium propanoate

chemical reaction in which long chain molecules are made by joinin many small molecules

Plastics

Alkenes

ethnes added together n times
~(C2H4)n~

Plastic bags

~(CH2CHCH3)n~

straws

~(CH2CHCl)n~

Pluming pipes, gutters

Polyvinyl chloride (PVC)

process of making useful corganic compounds from more simpler starting materials

• The reaction between ethene and clorine to form 1,2- dichloroethane(Intermediate compound)

• 1,2 dichloro ethae is cracked in hot conditions removing HCl (Elimatiion reaction) to from chloroethane (Intermediate)

• Polymerisation of chloroethane forms polychloroethane (PVC) ~(CH2CHCl)n~

Alcohols and carboxylic acids, they have a
-OH group, the h can be donated as a proton

Alcohols can act as acids only ehrn reacted with a very reactibe metals. (eg Li, K)
The -OH group of the alcohols belaves acidic and donates a proton.

C2H5OH + Na → C2H5ONa + 1/2H2

1) Inductive effect:
the Cδ+ attracts the Oδ- in OH
Oδ- in turn attracts electrons from Hδ+
Hδ+ is now more postive and will readily leave as a H+ ion.

2)stability of the Carboxylate ions
The carboxylate ion formed is very stable due to the delocalised nature of the pi electrons between each C---O bond

acid + carbonate --> Salt + water + Co2
procedure : using a spatula, sodium carbonate is added to ethanoic acid using a test tube.

Results: fizzing produced when bubbled through lime water.. will turn limewater milkey white

CO2

2CH3COOH + Na2CO3 --> 2CH3COONa + H2O + CO2

Sodium Ethanoate

No reaction, alchohols are very weakly acidic - only doate protons when reacted with group 1 alkali metals

Acid + metal --> salt + H2
Using thongs pick up a piece of Magnesium ribon and added to a test tube with ethanoic acid
Result : fizzing. Bubbles are ptoduced that will ignite with a pop

Hydrogen gas

2CH3COOH + Mg ---> (CH3COO)2Mg + H2

magnesium ethanoate

Carboxyic acid + alcohol --> ester + water (esterfication)
add some ethanol to a test tube. Using a dropper, a cm of ethanoic qcid and three drops of sulfuric acid are added and the test tube is placed in a hot water bath for 10 min
result - a fruity smell is observed, no colour change

CH3COOH + C2H5OH--[H+]-> CH3COOC2H5 + H2O

acts as a catalyst

Ethylethanoate

esters - esters have dinstinct fruity smell

all of the reactants ad products are colourless

esterfication