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10. Organic chemistry > Functional group chemistry > Flashcards

Functional group chemistry Flashcards

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1
Q

Why are alkanes unreactive?

A
  • C-H bonds are non-polar due to the small difference in electronegativity
  • All C-C and C-H are covalent bonds, hence very strong and kinetically stable
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2
Q

How do alkanes undergo combustion?

A
  • Complete combustion (excess O2) produces CO2 and H2O
  • Release large amounts of heat, hence used as fuels
    OR
  • Incomplete combustion (limited supply of O2)
  • Products: CO + H2O OR C (solid soot) + H2O
    Be able to balance these equations
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3
Q

What is free-radical substitution?

A
  • Reaction in which halogens replaces a hydrogen
  • Products: halogenoalkane + hydrogen halide
  • Photochemical reaction in which ultraviolet (UV) radiation is present
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4
Q

Why is UV radiation required in free-radical substitution?

A
  • Used in homolytic bond fission to break the bonds between a halide molecule into two free-radicals
  • They both have 7 electrons and hence are very reactive
  • It is a chain reaction as the free-radicals initiate the reaction
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5
Q

Explain initiation (1) and propagation (2) of the free-radical substitution.

A
  • In initiation, 1 reaction, the homolytic bond fission occurs when the halide molecule is separated into two free radicals by UV radiation
  • In propagation, 2 reactions, the alkane reacts with a free-radical. The free radical takes a hydrogen from the alkane. The product is a free radical alkane with 1 less H and a hydrogen halide
  • The free radical alkane reacts with a new halogen molecule (2) to form the product in which a hydrogen is replaced by a halide + a free radical
  • Free radical act as catalysts
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6
Q

Explain the termination (3) stage of free-radical substitution.

A
  • There are three possible outcomes:
    2 free radicals react to form dihalide, free alkane radical and halide radical react to produce the wanted product or 2 alkane radicals react to produce a new alkane
  • Essentially unpaired electrons join together to get rid of the free-radicals
  • This step stops the reaction
    Check book
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7
Q

Why are alkenes more reactive than alkanes?

A
  • Unsaturated (double bond)
  • Arranged in a trigonal planar (120°)
  • More reactive than alkanes due to C=C as there is a region of high electron density at the double bond which is where also chemical reactions take place
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8
Q

What type of addition reactions to alkenes undergo?

A
  • Hydrogenation
  • Hydration
  • Halogenation
  • Test for unsaturation
  • Addition polymerisation
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9
Q

Explain hydrogenation. Why is it used in industry?

A
  • alkene + H2 (g) —> alkane
  • Under high pressure and temperature (180°C)
  • Nickle catalyst required
  • Used in industry to make saturated compounds with high melting points (margarine)
  • Results in trans fats (health concerns)
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10
Q

Explain hydration.

A
  • alkene + H2O (g) —> alcohol

- Sulfuric acid (H2SO4) or phosphoric acid (H3PO4) catalyst required

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11
Q

Explain halogenation.

A
  • alkene + hydrogen halide —> halogenoalkane
  • at r.t.p
    OR
  • alkene + halogen —> dihalogenoalkane
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12
Q

Explain the test for unsaturation.

A
  • Used to distinguish between alkenes and alkanes
  • Halogen is added to both samples
  • Bromine water is added
  • Alkene decolourises the bromine, alkane mixture remains brown
  • Brown —> colourless
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13
Q

Explain addition polymerisation.

A
  • A reaction in which monomers join together to form a long chain called polymer
  • In a polymer there are repeating units
  • n represents a large number, number of repeating units
  • The chain is saturated
  • Prefix poly- the suffix -ene and in brackets the monomer e.g. poly(ethene)
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14
Q

What is the most common plastic polymer?

A
  • Poly(chloroethene) or PVC, which is the most used plastic

- Synthesis is associated with toxins such as the by-product dioxin

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15
Q

Explain and be able to draw the monomer, repeating unit and polymer.

A
  • The monomer is the structure that is in the brackets
  • Polymer is many monomers (without the double bond together)
  • Repeating unit includes the brackets and the n
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16
Q

What determines the physical and chemical properties of alcohols? Why are alcohols soluble?

A
  • The functional group (hydroxyl group OH)
  • Due to the H on the hydroxyl group, alcohols can form hydrogen bonds with other molecules and also with water
  • Therefore it can dissolve in water
17
Q

Do alcohols undergo combustion reactions?

A
  • Complete combustion (excess O2)
  • Incomplete combustion (lack of O2)
  • Enthaply change of combustion
18
Q

What classification of alcohols undergo oxidation reactions? How does oxidation occur?

A
  • Primary and secondary
  • Reaction with oxygen
  • Due to the presence of hydroxyl group and an oxidising agent
    E.g. potassium manganate (VII) from purple to colourless and acidified potassium dichromate (VI) from orange to green
19
Q

What is partial oxidation? How is the product extracted?

A
  • Only with primary alcohols
  • Oxidation with excess alcohol
  • Result: aldehyde
  • Aldehyde is removed by distillation as it has a lower boiling point (evaporates first) than the alcohol and carboxylic acid
  • Normal distillation
20
Q

What is complete oxidation? How is the product extracted?

A
  • Only with primary alcohols
  • Result: carboxylic acid
  • Conditions: heat under reflux and excess oxidising agent {O}
  • To obtain the carboxylic acid, the mixture is heated under reflux
  • Oxidising agent and alcohol vaporize and condense at the same time to complete complete oxidation
21
Q

What product is produced when secondary alcohols undergo oxidation? Why do tertiary alcohols not undergo oxidation?

A
  • Ketone, extracted under reflux and oxidising agent

- Tertiary alcohols have no hydrogen bonded to the carbon that is bonded to the hydroxyl group

22
Q

What are nucleophilic substitutions?

A
  • Esterfication and condensation reactions with carboxylic acids
23
Q

Explain esterfication.

A
  • Reaction between alcohols and carboxylic acids in condensation reactions
  • Product: ester and H2O
  • Reversible reaction (equilibrium)
  • Requires a strong acid catalyst e.g. sulfuric acid
24
Q

How do you name esters?

A
  • Alcohol name becomes alkyl group
  • Carboxylic acid follows ending with -oate
  • E.g. ethanol + ethanoic acid —> ethyl ethanoate
25
Q

What are properties of esters?

A
  • Volatile and have an odor

- Used in cosmetics, flavours and perfumes

26
Q

What are halogenoalkanes and what are their properties?

A
  • Compounds in which a hydrogen is replaced by a halogen atom
  • General formula: CnH2n+1X
  • More reactive than alkanes
  • Oily liquids and do not mix with water (inability to form hydrogen bonds)
27
Q

What type of reactions do halogenoalkanes undergo?

A
  • (Nucleophilic) Substitution reactions

- Heterolytic bond fission

28
Q

Why do subsitution reactions work in halogenoalkanes?

A
  • Group or one atom is replaced by another atom or group
  • The carbon-halogen bond is polar (due to the difference in electronegativity)
  • The bond is electro-deficient and can be attacked by nucleophiles
29
Q

What are nucleophiles?

A
  • Electron-rich species that contain lone pair of electrons and are attracted to regions of positive charge
  • They are attracted to the carbon-halogen bond for instance
  • They donate lone pair of electron to the electron-deficient carbon
30
Q

What is heterolytic bond fission?

A
  • Carbon-halogen bond breaks, one atom takes both of the bonding electrons which forms oppositely charged ions (halogen becomes negative)
31
Q

How does nucleophilic substitution work?

A
  • A hydroxide ion (OH-) is substituted from a strong alkali (e.g. potassium or sodium hydroxide) into the halogenoalkane
  • The OH- is the nucleophile and replaces the halogen to produce an alcohol
  • Due to the heterolytic bond fission, the halogen of the halogenoalkane takes both bonding electrons and reacts with the alkali from the alkali solution
  • Conditions: heat and dilute solution of a strong alkali
    e. g. CH3CH2Cl + NaOH –> CH3CH2OH + NaCl
32
Q

What determines the stability and type of reactions benzene undergoes?

A
  • Delocalised electrons within the structure ensure the stability and determine which reactions benzene undergoes
33
Q

What type of reactions does benzene undergo?

A
  • Substitution reactions with halogens
  • Electrophilic substitution reactions
  • Combustion reactions (same as in other hydrocarbons)
34
Q

What is a substitution reaction in benzene?

A
  • A hydrogen is replaced by an electrophile, this does not disrupt the ring structure which makes it more energetically favourable
  • Benzene does not undergo addition reactions as that would disrupt the structure
35
Q

What do delocalised electrons do in substitution reactions?

A
  • They provide a region of electron density, hence attract species called electrophiles where they react (in the inside ring of benzene)
36
Q

What are electrophiles?

A
  • Species that are electron deficient and have a (partial) positive charge
  • They are attracted to the delocalised electrons
37
Q

How does benzene undergo electrophilic substitution reactions?

A
  • The electrophile is a cation e.g. nitronium ion from a compound
  • Product e.g. nitrobenzene and H2O
  • Requires concentrated sulfuric acid as a catalyst
38
Q

How does benzene undergo substitution reactions with halogens?

A
  • The electrophile is a halogen e.g. Cl2
  • Product: halogenbenzene and hydrogen halide
  • Catalyst is aluminum halogen

10. Organic chemistry (2 decks)

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