Unit two - synthesis Flashcards Preview

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Flashcards in Unit two - synthesis Deck (32):

what is the process that occurs when bonds break ?

bond fission


what is the two types of bond fission that can occur ?

homolytic fission
heterolytic fission


explain homolytic fission

in this type of bond fission the shared electrons separate equally as one electron goes to each atom. occurs with non polar covalent bonds.This results in each atom containing an unpaired electron represented by a dot , this is a free radical. Each atom has a neutral charge as they have an equal number of electrons and protons.


what type of arrow is used to demonstrate homolytic fission and why?

a single headed curly arrow as it indicates the movement of a single electron


explain heterolytic fission

in this type of bond fission both the shared electrons go to one atom. This is more likely to occur when the covalent bond is polar. The electrons go to the most electronegative atom in the bond. This results in the atom becoming negatively charged that gained the electrons while the other atom becomes positively charged.


what is an electrophile ?

these are positively charged ion or neutral molecules that are deficient in electrons. They are capable of accepting electrons to form a covalent bond.


what are carbocations

a positively charged carbon atom , so they are electrophilic


what is a nucleophile?

this is a negatively charged ion or a neutral molecule that is electron rich. They are capable of donating electrons to form a covalent bond.


what type of arrow is used to demonstrate heterolytic bond fission ?

a full headed curly arrow as this shows the movement of an electron pair.


what is a carbonation ?

a negatively charged carbon ion , so is nucleophilic.


what occurs when alkanes are exposed to light ?

the alkane reacts slowly with halogens and a hydrogen halide is formed during a substitution reaction.


what is a hydrogen halide ?

a hydrogen bonded to a halogen I,e h-cl.


what are halogenoalkanes ?

it is when an alkane has had one or more of the hydrogen atoms replaced with a halogen atom.


how are halogenoalkanes named ?

the chain is numbered closest to the halogen. The number is written first of where the halogen is. then the halogen prefix is used. and then the basic compound chain is named. i.e methyl pentane.


how can alkenes be produced ?

cracking of an alkane
dehydration of alcohols
from monohalogenoalkanes


what catalyst is used to crack an alkane to produce an alkene ?

aluminium oxide catalyst


describe how dehydration of an alcohol leads to an alkene being produced.

the alcohol is mixed with conc acid ( h2o4 , or h3po4) this is then heated. water is eliminated to form the alkene.


describe how monohalogenoalkanes can form alkenes ?

the monohalogenalkane is reacted with potassium hydroxide dissolved in ethanol. This eliminates the hydrogen halide and the alkene is left.


what is the 2 main reactions that monohalogenoalkanes undergo?

nucleophilic substitution and elimination.


whats the 4 types of nucleophilic substitution a monohalogenoalknane can undergo ?

1. react with aqueous alkali to from an alcohol
2. react with alkoxide ion to form ethers
3. react with cyanide ion to form nitriles.
4. react with ammonia to form amines.


why do monohaloenoalkanes undergo nucleophilic substitution?

The halogen atom contains a higher electronegativity than the carbon atom. This results in a polar covalent bond being present and as a result the monohalogenalkane acts as an electrophile and is susceptible to attack by nucleophiles.


explain stages of nucleophilic substitution of monohalogenoalkanes.

the nucleophile attacks the monohalogenoalkane as this is acting as an electrophile The nucleophile donates a pair of electrons to the monohalogenoalkane and a covalent bond is formed between the c-x. At the same time the halogen atom is thrown out and the nucleophile replaces it.


what are SN1 and SN2 ?

reaction mechanisms present during nucleophilic substitution.


explain SN1

The S stands for a substitution reaction. The N stands for nucleophilic . And the 1 shows there is only one molecule involved in the rate determining step. There will be a two step reaction but only one reactant. There is a carbocation intermediate formed.


explain SN2.

The S stands for substitution. The N stands for nucleophilic . The 2 shows there is 2 molecules involved in the RDS. There will be a single step reaction with 2 particles. A negative transition state is formed.


what is the simplest and most important aromatic ?



what is benzenes formula ?



what was the kekule model ?

it supposed that the benzene structure was a ring with alternating double and single bonds.


why was the kekule structure incorrect ?

when bromine was added to bromine it did not declolorise quickly , therefore it is not unsaturated and doesn't contain c-c double bonds.
analysis of bond reveals that all the c-c bonds are of equal length. However , kekule model shows alternating bond lengths os single and double bonds.


why does benzene not undergo addition reactions but substitution reactions can occur ?

addition reactions would disrupt the delocalised electrons and affect the stability of benzene. however substitution reactions can occur without affecting the stability.


What reaction does benzene undergo and why ?

Electrophilic substitution as the delocalised ring of electrons make benzene susceptible to attack by electrophiles.


name the electrophilic substitution reactions benzene undergoes?

bromination = bromobenzene
chlorination = chlorobenzene
sulfonation = benzenesulfonic acid
nitration = nitrobenzene
akylation = methylbenzen