Basic concepts, alkanes and alkenes Flashcards
name of functional group added at the end for alkanes
- ane
name of functional group added at the end for alkenes
- ene
name of functional group added at the end for alcohols
- ol
name of functional group added at the end for esters
- oate
name of functional group added at the end for carboxylic acids
- oic acid
name of functional group added at the end for ketones
- one
name of functional group added at the end for aldehyde
- al
name of functional group added at the end for acid chlorides
- oyl chloride
name of functional group added at the end for amides
- amide
prefix for halogenoalkanes
chloro- bromo- or iodo-
prefix for amines
amino-
prefix for nitriles
cyano-
what is organic chemistry
the chemistry of carbon compounds
organic compounds are…
found naturally in living or once living things
the simplest organic compounds contain
C and H only
what may other organic compounds contain
O, N, F, Cl, Br, I and S
how are organic compounds usually bonded
covalently
what does carbon always form
4 bonds
what does H always form
1 bond
what does O always form
2 bonds
what does N always form
3 bonds
what do F Cl Br and I always form
1 bond
what does a structural isomer have
same molecular formula but different structural formula
what is a functional group
a group of atoms that gives a molecule its characteristic reaction
what are alkanes
- simplest organic compound
- contain c and h with single bonds only
what is a homologous series
a series of compounds with the same functional group where each successive member differs by CH2 and have similar chemical properties and a gradual change in physical properties
what is general formula
simplest algebraic formula of a member of a homologous series eg alkanes eg CnH2n+2
what is molecular formula
actual number of atoms of each element in a molecule eg C2H6O
what is structural formula
minimal detail that shows the arrangement of atoms in the molecule eg CH3OCH3
CH3CH2OH
what is displayed formula
the structure that shows the relative positioning of the atoms and all the bonds between them
what is skeletal formula
a simplified structure. H atoms are removed from what is drawn and C-C bonds are drawn as a line. functional groups remain
what is aliphatic
compounds containing C and H joined together in straight chains, branched chains or non aromatic rings
what is alicyclic
aliphatic compounds containing C and H jointed together in non aromatic rings
what is aromatic
a compound containing a benzene (arene) ring
what is a covalent bond
a shared pair of electrons between 2 atoms
for reactions to occur with organic substances…
covalent bonds must be broken
homolytic fission
- symmetrical bond breaking
- one electron from the bonding pair goes to each atom of the bond
- the products formed have an unpaired electron -> radicals
- the products are extremely reactive -> uncontrollable reactions
- each half headed arrow shows the movement of an electron from the bonding pair
heterolytic fission
- unsymmetrical bond breaking
- both electrons of the bonding pair goes to one atom of the bind
- positive and negative ions formed
- each curly arrow shows the movement of a pair of electrons
- the electron pair moves to the more electronegative element which becomes negatively charged
general formula of alkanes
CnH2n+2
cyclic alkanes
share the same general formula as alkanes, highly reactive and very unstable due to the strained ring
what are alkanes
- saturated hydrocarbons, contain C and H only with single bonds
- each C atom is joined to 4 other atoms by single covalent bonds - sigma bonds
when do sigma bonds form
when orbitals overlap directly between atoms
shape around carbon atom in an alkane
tetrahedral
- no lone pairs, electron pairs repel to max separation
- 109.5°
physical properties of alkanes
- low mp and bp - weak instantaneous dipole induced dipole interactions between molecules
- mp and bp increase with increased chain length - more electrons in the molecules so more/ stronger london forces.
greater surface area of contact between molecules so more london forces - mp and bp decreases with increased branching - molecules pack less well together so less SA of contact between molecules and so less/weaker london forces
alkanes and water
- insoluble in water as non polar molecules
- soluble in organic solvents
- less dense than water (float / upper layer in a mixture)
combustion of alkanes
all alkanes burn fully to produce CO2 and H2O
e.g CH4 + 2O2 -> Co2 + H2O
what happens if insufficient oxygen is available for combustion
Co and C instead of Co2 will be formed
Carbon monoxide is toxic as it binds to haemoglobin which prevents it from carrying o2 round the body
RCE of Free radical substitution
Reagents : Cl2 or Br2
Conditions : UV light as no reaction occurs in the dark
Equation: eg CH4 + BR2 -> Ch3Br + HBr
Initiation stage of free radical substitution
Br2 -> 2Br•
Homolytic fission forming Br• radicals. Incredibly reactive and lead to a chain reaction forming many products which is hard to control
Propagation stage free radical substitution
Ch4 + Br• -> •Ch3 + Hbr
• Ch3 + Br2 -> Ch3Br + Br•
Each propagation step consumes one radical and generates one radical to allow the chain reaction to continue. Many products are possible here as more than one H atom can be substituted
termination stage free radical substitution
•CH3 + Br• -> Ch3Br
•Ch3 + •Ch3 -> C2H6
each reaction consumes 2 radicals breaking the chain reaction
why are radical substitution not a good way to produce a specific product
- propagation steps difficult to control and can lead to a wide range of products as more than 1 H atom can be substituted as well as substitution in different positions
- Br is regenerated in the 2nd propagation step and so a small number of Br molecules initially can lead to a large number of alkane molecules reacting
- Radicals are extremely reactive, reacting with almost any species they collide with
when is most of the product is made
during the propagation steps
what is a radical
species with an unpaired electron in a mechanism
what is substitution
one atom / group replaced by another atom / group
reactions of cycloalkanes
generally just the same as alkanes, with the exception of the very small ones, especially cyclopropane
extra reactivity of cyclopropane with uv light
with UV light radical substitution the reaction occurs with cl2 or br2 in the same way as a non cyclic alkane
extra reactivity of cyclopropane without uv light
can undergo addition reactions (alkenes theory) which other alkanes cant.
this can still happen in the presence of light but will get substitution reactions as well
what happens without uv light to the ring of cyclopropane
the ring is broken due to being very strained - the bond angles are 60 rather than 109.5 when carbon makes its four single bonds
why is the ring unstable and how can it be made more stable in cyclopropane
the overlap between the atomic orbitals in forming the carbon carbon bonds is poorer than normal and there is considerable repulsion between the bonding pairs. the system becomes more stable if the ring is broken
general formula of alkenes
cnh2n
bonding of alkenes
they are unsaturated hydrocarbons so contain c and h only with 1 or more c=c double bonds
what do each carbon atom of the double bond form
3 sigma bonds. the 4th electron of each carbon is in the P orbital, perpendicular to the plane of the molecule. they overlap sideways above and below the bonding atoms to form the pi bond
what is a pi bond
sideways overlap of p orbitals and below bonding c atoms
what is a sigma bond
end on overlap of orbitals between bonding atoms
what is the shape around each carbon atom of the double bond
trigonal planar
c2h4 structure and bonding
trigonal planar
3 bonding centres - 2 single 1 double
electron pairs repel to max separation
bond angle 120 degrees
restricted rotation as a result of pi bonding
restricted rotation about the c=c double bond. rotating this bond would mean breaking the pi bond which would require a lot of energy. keeps the molecule in a rigid flat structure
what allows e/z isomerism
the restricted rotation keeping it rigid and flat structure
length and strength of c=c due to pi bonding
c=c is shorter than c-c as 4 electrons attracted by the 2 nuclei of the bond instead of 2. c=c is stronger as it has both pi and sigma bonds giving it a greater total bond enthalpy
why are alkenes more reactive
relative low bond enthalpy of the pi bond means it is broken more easily
why is electrophilic attack possible
due to the region of high electron density (pi bond) above and below the bond
mp and bp of alkenes
increase with increasing chain length. mp and bp lower than corresponding alkanes - alkenes cant pack together as efficiently so fewer London forces are established and less energy required to break
alkenes soluble or insoluble
insoluble
what are the main reactions of alkenes
electrophilic addition reactions
what is an electrophile
molecule or positive ion that can accept a pair of electrons to form a covalent bond
what is an addition reaction
2 molecules react to form 1
why is the double bond open to electrophilic attack
it is electron rich
hydration alkene
reagent: steam
conditions: h3po4 catalyst 300°c 60atm
observations: no visible change
bromination alkenes
reagent: bromine (aq or inert solvent)
condition: room temperature
observations: orange bromine water turns colourless
mechanism for bromination
- br2 is polarised as it approaches double bond
- curly arrow goes from e- rich to e- deficient area. shows movement of e- pair
- bond breaking is heterolytic -> both e-s go to 1 atom of the bond
reaction with hcl alkenes (also same as HBr or HI)
Reagent : HCl gas or conc solution
Conditions: room temperature
observations: no visible change
what rule is for unsymmetrical alkenes
markownikoff rule with major and minor product
explanation of electrophilic addition
- an alkyl group donates electron density to any carbon atom to which it is attached (alkyl groups are electron donating)
- this means that the carbonation with the most alkyl groups attached will be the most stable
- the electron donating alkyl groups stabilise the positive charge by allowing it to be more spread out
reasoning for something being the major product
…… is the major product due to the carbocation intermediate it forms via being more stable
hydrogenation alkenes
used in the production of margarine from vegetable oil
reagent: hydrogen gas
conditions: nickel catalyst
observations: no visible change
equation for hydrogenation
c2h4 + h2 -> c2h6
addition polymerisation
many monomers join together to form a polymer (long chain molecule)
pi bonds break and many molecules join together
synthetic polymers
- made from oil derived alkenes and replacing many natural materials
- non biological so difficult to dispose of
- use up landfill space
- produce toxic fumes when burnt
how can sustainability be improved
- burn polymers to produce heat energy for electricity generation. this conserves fossil fuel supplies
- removal of toxic waste products from burning
halogenated plastics form HCl on burning, removed with a base - recycling to form new products
- use polymers as an organic feedstock for the production of new plastics and organic chemicals. monomers and other substances can be reclaimed from waste polymers resulting in mixtures similar to crude oil
- develop biodegradable and photodegradable polymers. broken down by microorganisms or have bonds that are weakened when exposed to light.
- develop polymers made from plant based materials eg maize and starch to reduce demand of finite oil reserves
ether properties and uses
brittle and cheap
plastic bags
polypropene properties and uses
stronger than polyethylene
used for plastic kitchenware eg buckets
polychloroethene uses
flexible and strong
drain pipes and phone cables
phenylethene properties and uses
brittle and cheap
polystyrene - packaging and cups
polytetrafluoroethene properties and uses
non stick frying pans
teflon
what is a stereoisomer
compounds with the same structural formula but with a different arrangement in space
e/z isomer definition
an example of stereoisomers. restricted rotation about the c=c double bond and 2 different groups attached to each carbon atom of the c=c double bonds
cis-trans isomers
a special case of e/z isomerism where 2 of the groups attached to each carbon atom of the c=c double bond are the same
for e/z isomerism must have
restricted rotation and 2 different atoms or groups
trans
across (E)
cis
same size Z
