4.1 Basic Concepts And Hydrocarbons Flashcards
General formula
An algebraic formula that can describe any member of a family of compounds
Empirical forumla
Simplest whole number ratio of atoms of each elemnt in a compound
Molecular formula
Actual number of atoms of each element in a molecule
Structurual forumla
Like for Butan-1-ol
Shows arrangement of atom carbon by carbon, with the attached hydrogen and functional group
CH3CH2CH2CH2OH
or
CH3(CH2)30H
Skeletal formula
Shows the bond of the carbon skeleton only, with any functional groups. The hydrogen and carbon atoms aren’t shown. (zig zag and ring ones)
Displayed forumla
Shows how all the atoms are arranged, and all the bonds between them
Branched alkanes prefix or suffix
General formula for alkanes?
alkyl-(-yl)
CnH2n+2
haloalkanes prefix or suffix
chloro-/bromo-/iodo-
aldehyde prefix or suffix
-al
ketones prefix or suffix
General formula for ketones?
-one
CnH2nO
cycloalkanes prefix or suffix
General formula for cycloalakane?
cyclo-…-ane
CnH2n
carboxyclic acid prefix or suffix
General formula for carboxcylic acid?
-oic acid
CnH2n+1COOH
ester prefix or suffix
alkyl-…-anoate
Structural isomers
Compounds with the same molecular formula but different structural formula
Homolytic fission
Breaking a covalent bond to form two radicals
Where each bonding atom is receiving one electron from the bonded pair
Heterolytic fission
Breaking a covalent bond to form two oppositely charged ions
where one bonding atom receives both electrons from the bonded pair
Curly Arrow
Shows the movement of an electron pair during a reaction
What are the 3 steps in free radical substitution
- initiation
- propagation
- termination
what is the initiation equations for methane and chlorine to give chloro-methane and hydrogen chloride
CL2 –> 2CL.
what are the 2 propagation equations for methane and chlorine to give chloro-methane and hydrogen chloride
Cl. + CH4 –> CH3. +HCl
Cl2 + CH3. –>CH3Cl +Cl.
what are the termination step equations for methane and chlorine to give chloro-methane and hydrogen chloride
Cl. + Cl. –> Cl2
Cl. +CH3. –>CH3Cl
CH3. + CH3 –> C2H6
Why do branch isomers have lower MP then straight chained isomers?
Can’t pack close to each other and smaller molecular surface areas
so less surface contact between molecules…
less induced dipole forces…
so less energy to break force
Why does BP increase as chain lengths increase for hydrocarbons?
Stronger intermolecular forces
Why does adding carbon to a chain start to become less significant in terms of boiling point?
As the mass is increasing by a small percentage each time
Homologous series
A series of organic compounds having the same functional group but with each successive member differing by CH2
Functional group
A group of atoms responsible for the characteristic reaction of a compound
What are the general formula for alkenes and alcohols?
Alkene: CnH2n
Alcohol: CnH2n+1 OH
Aliphatic
A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings (have no benzene ring)
Alicyclic
An aliphatic compound arranged in non-aromatic rings with or without side chains (have a ring but not a benzene ring)
Aromatic
A compound containing a benzene ring
What is meant by a saturated compound?
Single carbon-carbon bonds only
Unsaturated compound
The presence of multiple carbon-carbon bonds, including c=c bonds, c-c and aromatic rings.
Describe alkanes
Saturated hydrocarbons containing single C-C and C-H bonds as sigma bonds; free rotation of the sigma bond
What is a pie bond?
Sideways overlap of adjacent p-orbitals above and below the bonding C atoms.
What is an electrophile?
An electron pair acceptor
What is a radical?
A species with an unpaired electron
What shape and bond angle is around a carbon in an alkane?
tetrahedral, 109.5, because of 4 bonding pair electrons repelling each other equally
Whats the equation for combustion of propane?
C3H8(g) + 502(g) –> 3C02(g) + 4H20(g)
Combustion reactions happen between what state?
and what does this mean has to happen first?
Gases, so liquid alkanes must be vaporised first.
Smaller alkanes are more volatile, so they’ll burn more easily too
What releases more energy larger alkanes or smaller alkanes and why?
larger alkanes releases lots more energy per mole as they have more bonds to react. So alkanes are excellent fuels
Whats the danger when alkanes burn in limited oxygen?
CO is produced. It is poisonous.
Why is CO (carbon monoxide) poisonous?
CO is better at binding to haemoglobin than oxygen, so it binds before the oxygen can. so less oxygen is being carried around body, leading to oxygen deprivation.
Whats required for free radical substitution?
UV light-photo dissociation
What are the problems with free radical substitution?
The problem with this is further substitution can occur and substitution can occur in different positions in molecules with more than 1 carbon
Describe an alkene
unsaturated hydrocarbons containing C=C compromising of a π-bond and σ-bond
What is a σ-bond?
σ-bond: Overlap of orbitals directly between the bonding atoms
What is a π-bond?
π-bond: Sideways overlap of adjacent p-orbitals above and below the bonding C atoms
What is the shape and bond angle around a C=C?
Trigonal planar shape, 120 degrees, 3 bonding pairs, no lone pairs, electron pair repulsion theory (the double bond counts at 1 electron pair)
What is weaker π-bond or σ-bond?
- π-bond are much weaker because the electron density is spread out above and below the nuclei.
- This means that the electrostatic attraction between nuclei and shared pair of electrons is weaker,
- so π-bond have relatively low bond enthalpy.
Why are alkanes not as reactive as alkenes?
Only contain C-C and C-H σ bonds, which have high bond enthalpy and so are difficult to break
The bonds are also non polar so they don’t attract nucleophiles or electrophiles
Why are alkenes more reactive?
C=C contain both π-bond and σ-bond
The C=C contain 4 electrons so it has a higher electron density and the π-bond also sticks out above and below the rest of the molecule
These 2 facts mean π-bond is likely to be attacked by electrophiles
The low bond enthalpy of the π-bond also contribute to reactivity of alkenes
What industry make use of the highly reactive alkenes?
Petrochemical
What is a steroisomer?
same structural formula but different arrangement in space
E/Z isomerism
an example of stereo isomerism, due to restricted rotation about a double bond and two different groups attached to each carbon atom of the C=C group
Cis–trans isomerism
A special case of E/Z isomerism in which two of the substituent groups attached to each carbon atom of the C=C group are the same
How do you identify E/Z stereoisomer
- First see if its a steroisomer (when two double bonded carbon atoms each have 2 different atoms or groups attached)
- Its E if the highest priority (look at atomic mass) groups are diagonal
its Z if highest priority are both above or both below the c=c
How do you identify if its cis or trans?
cis identical groups are on the same side of the c=c
Trans identical groups are on opposite side of the c=c bond
Describe addition reaction of alkenes with hydrogen reagent: condition: Product: Equation: use:
reagent: hydrogen
condition: Nickel catalysts, 150.c
Product: Alkane
Equation: C2H4(g) + H2(g) –> C2H6(g)
use: Margarine manufacture
Describe addition reaction of alkenes with steam reagent: condition: Product: Equation: use:
reagent: Steam
condition: catalyst-phosphoric acid, 300.c, 60-70 atm
Product: alcohol
Equation: C2H4(g) + H20 (g) C2H50H
use: Ethanol manufacture
What tests for the presence of a double C=C?
Bromine
Shake an alkene with orange bromine water,, the solution quickly decolourises
This is because bromine is added across the double bond to form a colourless dibromoalkane
How does electrophilic addition reactions happen?
The double bond has got plenty of electrons and is easily attacked by electrophiles
electrophiles are electron pair acceptors
electrophiles include positively charged ions (H+, N02+) and polar molecules
Halogen and alkene form…
What type of reaction is it?
Dihaloalkane
Electrophilic addition reaction
What is a carbocation?
Organic ion containing a positively charged carbon atom
Describe the mechanism for halogen bromine reacting with ethene
The double bond repels the electrons in Br2, Polarising Br-Br
Heterolytic fission of Br2. The closer Br gives up the bonding electrons to the other Br and bonds to the C atom. (Arrow from double bond to Slightly positibe Br, arrow from Br-Br bond to slight negative Br
You get positively charged carbocation intermediate
The Br- now zooms over (show unpaired electron pair on Br with negative charge, draw arrow from electron pair to + on carbocation)
and bonds to the other C atom forming
1, 2-dibromoethane
What’s markonikoffs rule?
The major product from addition of a hydrogen halide (HX) to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attachedx
Whats most stable, tertiary, secondary or primary cation?
Tertiary carbocation intermediate
Whats useful about polymers?
Very un-reactive so good for pans window coating frame
How are plastics disposed of?
organic feed stock, combustion, recycle, landfill
OCRL
Why does burning waste plastics need to be carefully controlled?
To reduce toxic gasses
polymers that contain chlorine (such as PVC) produces HCl when burned
Waste gasses is passed through scrubbers which neutralise gases like HCl by allowing them to react with a base.
How can biodegradable polymers made decomposable?
renewable raw materials such as Starch or oil fractions,
Photo-degradable polymers what are they?
polymers that decompose when exposed to sunlight
