CH6: Organic Chemistry I Flashcards by Ashwarya Magon

What are isomers? And the 2 types?

Molecules that have same molecular formula, but atoms arranged differently
2 types :
Structural
Stereoisomers

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What is a structural isomer and the 3 types?

Compound with same molecular formula, but structural formula is different
1. CHAIN ISOMERS
Carbon skeletons is arranged differently (straight chain or branched) - so have similar chemical properties, but physical properties (BP /MP ETC) are different due to to different shape

POSITIONAL ISOMERS
Functional group attached to different carbon atom - physical/chemical properties are different
FUNCTIONAL GROUP ISOMERS
Same atoms can be arranged into different functional groups - physical/chemical properties are different

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General forumula of alkanes ?

CnH2n+2
Saturated hydrocarbons - all C-C bond are single bonds

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What is bond fission and the 2 types?

Breaking of a covalent bond

HETEROLYTIC FISSION - bond breaks unevenly , with one the bonded atoms receiving both electrons
- forms CATION and ANION (bc one gain electrons , the other loses it )

HOMOLYTIC FISSION - bond breaks evenly/each bonding atoms receives one electron
- forms 2 radicals (particles that have an unpaired electron)

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How are halogenoalkanes formed from alkanes? What are the 3 stages?

Halogens react with alkanes in PHOTOCHEMICAL reactions - started by light
- hydrogen atom is substituted by chlorine/bromine - RADICAL SUBSTITUTION REACTION

3 stages to process :
Initiation
Propagation
Termination

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What is the initiation stage ?

UV lights breaks the Cl-Cl or Br-Br bond
- produces 2 radicals in homolytic fission reaction

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What is the propagation stage?

Radicals are used up/ created in a chain reaction
- free radicals will react with unreative alkanes to form an ALKYL RADICAL and hydrogen halide

this radical can attack another chlorine/bromine to from a halogenoalkane/regenerate chlorine/bromine free radicals

Cl. + CH4 —> CH3. + HCl
CH3 . + Cl2 —> CH3Cl + Cl.

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What are termination reactions ?

2 radicals join together to make a stable molecule

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What are the problems of free radical substitution?

Further substitution
Excess chlorine reacted with methane in the presence of UV light - causes further substitution and could produce CH2Cl2, CHCl3, CCl4
- nuisance because have to separate chloromethane from 3 unwanted products

Substitution of different carbon atoms - causes mixture of structural isomers

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What is cracking?

Breaking lager hydrocarbons into smaller , more useful hydrocarbon fractions

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What re the 2 types of cracking?

Thermal cracking - requires high temps(1000C)/pressure (70 atm) produces a lot of ALKENES

Catalytic cracking - lower temps(450 C)/pressure , but need catalyst (aluminium oxide/zeolite) to produce aromatic hydrocarbons

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What is reforming and why do we need to do this?

Reforming : Converting straight chain alkanes into branched chain alkanes /cyclic hydrocarbons

Needed because : straight chan alkanes are more likely to explode , rather than combust , when compressed in engine —> CAUSE KNOCKING

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How does complete/incomplete combustion of ALKANES cause pollution?

Complete combustion : forms CO2and H2O
Incomplete combustion: forms CO , Cand H20

Burning alkanes can also form :
- unburnt hydrocarbons - react with NO2 and SO2 to produce PAN in photochemical smog
- carbon particulates
- sulfur/nitrogen oxides

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How s carbon monoxide harmful?

Toxic and odorless gas
- binds to haemoglobin in blood before oxygen can
- so oxygen deprivation in body

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How are oxides of sulfur/nitrogen harmful?

Fuels containing sulfur are burnt forming SULFUR DIOXIDE GAS —> converted into sulfuric acid

High pressure/temp in car engines cause NITROGEN OXIDES TO FORM —> converted into nitric acid

BOTH CAUSE ACID RAIN - destroys environment /plants/buildings
- makes rivers acidic - harmful to aquatic animals

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How are particulates harmful ?

Carbon particles (particulates ) from incomplete combustion FORM SOOT

damage lungs /cause respiratory problems
damage buildings - corrode them
global dimming

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How are catalytic converters used to remove pollutants ?

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use platinum catalyst to change into harmless/less harmful gases

Eg : 2NO + 2CO —> N2 + 2CO2
Nitrogen monoxide and carbon monoxide converted to nitrogen and carbon dioxide
NO is REDUCED
CO is OXIDISED

What are biofuels and the 3 types?

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Renewable fuels
BIODIESEL - made by refining renewable fats/oils
BIOETHANOL - made by fermentation
BIOGAS - made/released when organic waste breaks down

Why are biofuels seen as carbon neutral ?

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Bc CO2 produced from biofuels is absorbed by plants for growth
biodiesel/biogas can be made from waste that would go to landfill
biofuels can provide money for LEDCS , as they have space to grow crops needed , as less land needed for fuels

Drawbacks of biofuels ?

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cost of converting engines/machinery for biofuels instead of petrol/diesel
countries don’t have space to produce plants to make biofuels , bc needed for food production
rainforest cut down to provide land
shortage of fertile soils

Fractional distillation of crude oil?

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Crude oil is vaporised to 350 degrees
Enters column and gets cooler as you go up
Larger alkanes , have larger BP so condense lower
Smaller alkanes , have lower BP do condense higher up
Largest hydrocarbons have to high BP so don’t condense —> residue at bottom
Smallest hydrocarbons also don’t condense BP too low so drawn off as gases at top

What are sigma bonds?

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formed when 2 orbitals overlap , in straight line, in space between 2 atoms
gives highest possible electron density between positive nuclei
leads to strong electrostatic attractionbetween nuclei/shared pair of electrons
HAVE HIGH BOND ENTHALPY

What is a pi bond?

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Formed from sideways overlap of adjacent p orbitals
- electron density is spread out above/below the nuclei
- causes weaker electrostatic attraction between nuclei and shared pair of electrons , than sigma bond
- LOW BOND ENTHALPY

What is a double bond made up of?

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A sigma bond and pi bond

What are stereoisomers?

Compounds that have same structural formula but **different arrangement of atoms** in space. - because of **lack of rotation around double bond** (due to way p orbitals overlap to form Pi bond) mean one isomer cannot be switched to another

What is a E/Z isomer ?

E (trans) isomer have groups on **opposite sides** of double bond /carbon ring Z (Cis) isomer have groups on **same side**of double bond/carbon ring

How to work out if isomer is E or Z if all carbons have different groups attached to them?

Using Cahn-Ingold-Prelog (CIP) priority rules - look at atomic number of first atom attached to CARBON - higher the atomic number, the **higher the priority** - if high priority on same side - Z isomer - if high priority on opposite sides - E isomer

What’s an electrophilic addition ? What reactions are electrophilic addition?

The addition of an electrophile to a double bond - double bond opens up / atoms added The addition of : Hydrogen Steam Hydrogen halide Halogen

What are electrophiles?

Electron pair acceptors - short of electrons ,sp attract to areas with many electrons - positively charged ions /polar molecules

Conditions and reaction of HYDROGEN + ALKENE? How is this used in margarine manufacturing?

- produce ALKANE Conditions : NICKEL catalyst 150 degrees Margarine is made by **hydrogenating unsaturated** veg oils . By **removing double bonds**, you **increase MP** of oil so its solid at room temp

HALOGEN + ALKENES - reaction?

Form **dihalogenoalkanes** - halogens are added across the double bond

Test for alkenes?

Add bromine water (brown/orange) solution will **decolourise** if alkene is present - because bromine is added **across double bond**so goes colourless and forms dibromoalkane

STEAM + ALKENE - reaction and conditions

Forms alcohol Conditions : 300 degrees 60-70 atm Phosphoric acid catalyst

ALKENES + HYDROGEN HALIDES - reaction?

Form HALOGENOALKANES - if hydrogen halide is added to **unsymmetrical alkene**- 2 products - the amount of each product depends on how stable the carbocation is - carbocations with more alkyl groups are more stable - they feed electrons towards + CHARGE (Tertiary is most stable - so more of this made)

Oxidation of alkenes using ACIDIFIED POTASSIUM MANGANATE (oxidising agent)

C2H4 + H2O + [O] —> C2H4(OH)2 - the **purple solution turns colourless** Produced **DIOL**- alcohol with 2 -OH groups - this can be used to **test for alkenes**, as alkanes don’t have double bonds, so wont oxidise this way

What is addition polymerisation? And what are polymers?

Where monomers (containing at least one C double bond) , form long chains of polymers - **double bond opens up** Polymers - long chain molecule made up of **repeating units** (monomers)

Ways of disposing polymers?

RECYCLING : reduce amount of waste going to landfill sites - reduces use of finite resources Some can be recycled by **MELTING/REMOULDING** Some can be **CRACKED**into monomers/ used as ORGANIC FEEDSTOCK BURNED : if can’t be recycled (due to chemical composition ) , can be burned to **generate electricity** - needs to be controlled to **reduce toxic gases** E.g PVC contain chlorines so forms HCl - **scrubbers** can neutralise gases like HCl

Principles for sustainable polymer manufacturing?

- use **safe/environmentally friendly reactants** - use **fewer chemicals**/other materials - use **renewable** raw materials - **use catalysts** - keep energy use to minimum - **limit waste** products - produce polymers with **long lifespan**

What are biodegradable/compostable polymers ? Ands what are the advantage of these?

***Biodegradable***- Polymers that **naturally decompose** - products can be used for other applications - can be made from **renewable raw materials**, so **wont run out** BUT SORTING/COLLECTING MEANS ITS MORE EXPENSIVE THAN NON BIODEGRADABLE OPTIONS ***Compostable*** - polymers that are **plant based** - CO2 released in decomposition is same as CO2 absorbed by plant, so **not adding to CO2 in air** - **save energy** compared to oil based plastics

What are catalytic converters made from?

Ceramic honeycomb structure coated with a thin layer of catalyst metals (platinum, palladium,rhodium) —> give larger SA

Advantage of biofuels ?

Reduction of use of fossil fuels (which are finite) Biofuels are renewable More carbon-neutral Allows for fossil fuels to be used as feedstock for organic compounds cause less pollution than fossil fuels

CH6: Organic Chemistry I Flashcards

(41 cards)