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Chemistry > Topic 18 Chemistry > Flashcards

Topic 18 Chemistry Flashcards

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1
Q

What type of molecule is a Benzene aliphatic or arene

A

Arene/aromatic

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2
Q

What is the molecular formula for Benzene

A

C6H6

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3
Q

Describe why Benzene has a delocalized ring of electrons

A

In each Benzene molecule there are 6 carbon atoms in a hexagonal ring with one Hydrogen bonded to each carbon atom. Each carbon atom is bonded to two other carbons and one hydrogen by single covalent bds. So there is one unused electron on each carbon atom in a p orbital perpendicular to the ring. The six p electrons are delocalised above and below the plane of carbon atoms

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4
Q

Describe why the kekule model is incorrect

A

The kekule model is incorrect as it suggests that there are alternate c=c and c-c bonds meaning there would be two different bond lengths however x-ray diffraction shows us all bond lengths are the same

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5
Q

What are the enthalpies of hydrogenation for cyclohexane and a non delocalised structure with 3 double bonds and benzene. State their equations

A
  1. Cyclohexene + H2 > Cyclohexane - The enthalpy vahnge = -120 kj/mol
  2. Non deloclaised structure + 3H2 > hexagon - enthalpy change = -360 kj/mol
  3. Benzene + 3H2> hexgon enthalpy change= -208 Kj/mol
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6
Q

What are the enthalpies of hydrogenation for cyclohexane and a non delocalised structure with 3 double bonds and benzene. State their equations

A
  1. Cyclohexene + H2 > Cyclohexane - The enthalpy vahnge = -120 kj/mol
  2. Non deloclaised structure + 3H2 > hexagon - enthalpy change = -360 kj/mol
  3. Benzene + 3H2> Cycohexane enthalpy change= -208 Kj/mol
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7
Q

What type of reactions does benzene usually undergo and why

A

It usually undergoes electrophilic substitutions (due to its high electron density) and not addition reactions. Benzene has a delocalised electron system so addition reactions would involve breaking this system which does not happen so instead one hydrogen atom will be substituted for another atom

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8
Q

What is meant by delocalisation energy

A

The increase in stability of a molecule due to delocalisation of electrons

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9
Q

Name the 7 derivatives of benzene

A
  1. Methylbenzne
  2. Ethyl benzene
  3. Chloro benzene
  4. Bromobenene
  5. nitrobenzene
  6. benzene carboxylic acid
  7. benzaldehyde
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10
Q

How do you name aromatic compounds

A

If two or more substituents are present on the benzene ring we indicate their position by numbers ensuring that the lowest possible numbers are given. When two or more substituents are used they are written in alphabetical order and we use di or tri prefixes if necessary

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11
Q

What can benzene also be written as when it is regarded as a substituent side group

A

A Phenyl group (C6H5-)

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12
Q

What is a property of Benzene

A

Benzene is a carcinogen

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13
Q

Write the molecular formula for the complete combustion of Benzene

A

C6H6 + 7.5 O2 > 6CO2 + 3H20

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14
Q

Write the molecular formula for the incomplete combustion of Benzene

A

C6H6 + 4.5 O2 > 2CO2 + 2C + 2CO + 3H20

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15
Q

State the type of mechanism, the conditions, the reagents for the formation of bromobenzene from benzene.

A 
Mechanism= Electrophillic substitution 
Conditions= FeBr3 catalyst 
Reagents= Bromine
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16
Q

State the type of mechanism, the conditions, the reagents for the formation of bromobenzene from benzene.

A

Mechanism= Electrophillic substitution

Conditions= FeBr3 catalyst

Reagents= Bromine

17
Q

What is the equation for the formation of the electrophile cl+ and the electrophile Br+

A

CL= AlCl3 + Cl2 > AlCl4- + Cl+

Br= FeBr3 + Br2 > FeBr4- + Br+

18
Q

Write the equation for the reformation of the catalyst FeBr3

A

FeBr4- + H+ > Febr3 + HBr

19
Q

What is a phenol

A

A phenol is a benzene attached to an OH group directly, In a phenol the lone pair of electrons on the oxygen of the OH group interfere with the delocalised electron ring and the lone pair electrons becomes delocalised into the ring increasing the electron density of benzene

20
Q

What is the effect of side groups being attached into benzene

A

The side groups attached to benzene release electrons into the delocalised system making a higher electron density in the benzene ring so it becomes more attractive to electrophiles so benzene will carry out the substitution reactions more readily with milder conditions

21
Q

What is the name of the type of mechanism, the reagents and the electrophile involved in the nitration of benzene and conditions

A

Mechanism= Electrophillic substitution

Reagents = Conc HN03 and Conc H2SO4 (catalyst)

Electrophile = NO2 +

Conditions= 50 degrees

22
Q

What temperature is the nitration of benzene done at and why

A

It is done at 50 degrees to prevent polysubstitution so only one nitro group attaches

23
Q

What is the reaction, reagents, conditions and type of reaction for the hydrogenation of benzene to form cyclohexane

A

Reagents= Hydrogen (3H2)

Conditions= Nickel catalyst at 200 C and slight pressure (30atm)

Type of reaction = Addition and reduction

24
Q

What type of alkane is used in an friedel crafts alkylation reaction

A

Any chloroalkane

25
Q

What is the type of mechanism, the reagents, the conditions, and change in functional group in the alkylation friedel crafts reaction

A

Mechanism= Electrophillic substitution

Reagents = Chloroalkane in the presence of anhydrous aluminium chloride catalyst

Conditions= heat under reflux

26
Q

Write the formation of the electrophile for a reaction between chloroethane and benzene

A

AlCl3 + CH3CH2CL > CH3CH2+ + ALCL4-

27
Q

What is the name of the type of mechanism, the reagents, the conditions and the change in functional group for a friedel crafts acylation reaction

A

Mechanism= Electrophillic substitution

Reagents = Acyl chloride in the prescience of anhydrous aluminium chloride catalyst

Conditions= 50 degrees and heat under reflux

28
Q

Write the equation for the formation of the electrophile for a reaction between benzene and ethanoyl chloride.

A

AlCl3 + CH3COCL > CH3CO + + ALCL4-

29
Q

Draw the molecular formula of the reaction between phenol and bromine water and state the conditions

A

Phenol + 3 Br2 > Phenol structure + 3 Brs attached + 3HBR

30
Q

State some uses for phenols

A

They are used in the production of plastics antiseptics,disinfectants and resins for paints

31
Q

What is the equation for the formation of the electrophile No2+ for the nitration of benzene

A

HNO3 + 2H2SO4 > 2HSO4- + NO2+ + H3O+

32
Q

Whta is the equation for the reformation of the catalsts H2SO4

A

HSO4- + H+ > H2SO4

Chemistry (20 decks)

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