Organic chemistry Flashcards
What are the two types of isomers
Structural isomers
stereoisomers
What are the two types of structural isomers
Structural isomers are isomers with the same molecular formula bonded together in different arrangements, chain and positional isomers
What are chain isomers
They are the consequence of a branching alkyl group
What are positional isomers
They can occur for organic molecules that contain functional groups, the functional group can be attached to a different location
What are stereoisomers
They are isomers in which the atoms in two molecules are connected in the same order but have different arrangements in space
Do stereoisomers have different chemical properties?
They differ in their 3D shape and they can have very different chemical properties
What are optical isomers
They have a different placement of groups around one atom in a molecule. The molecules have identical molecular and semistructual formal.
Are optical isomers chiral
Optical isomers are said to be chiral, two objects are chiral when they are mirror images of each other and the mirror images cannot be superimposed
What area chiral objects
Chiral objects have mirror images which are superimposable
What is the requirement for a chiral molecule
A carbon atom joined to four different groups in a tetrahedral arrangement.
What are a pair of chiral molecules called
Enantiomers
What difference is there between the properties of chiral molecules
Enantiomers have identical physical properties apart from the way they rotate plane polarised light. Same melting and boiling points and the same solubility in water.
What are geometric isomers
These isomers occur where restricted rotation can occur about a carbon carbon double bond. Cis trans isomers
Define flash point
The lowest temperature at which a liquid will produce a vapour that will ignite to produce a flame when an ignition source is applied
What happens to hydrocarbons physical properties are molar mass increases
As Mr increases dispersion forces become stronger. Bp increases, viscosity increases, flashpoint increases, volatility decreases
What happens to physical properties of isomers with branches compared to non branched isomers
Liner isomers: they are more compact, molecules are closer and they have stronger intermolecular forces, dispersion forces.
Non liner isomers: as the molecule are far apart, weaker intermolecular forces, dispersion forces. Boiling point decreases, viscosity decreases, volatility increases, flashpoint decreases
What do stronger intermolecular forces cause
Greater boiling points, greater flash points and high viscosity and lower volatility
Do hydrocarbons dissolve in water
Hydrocarbons are on polar, therefore they do not dissolve in polar h2O, it simply forms a layer of separation. The top layer is hydrocarbons and h2o is denser
What is the difference in physical properties from an alkene to an alkyne
Mr decreases, therefore weaker dispersion forces. Physical properties decreases expect for volatility
What is the difference between physical properties from hydrocarbons and haloalkanes
the carbon chlorine bond in chloromethane is polar because the chlorine atom is more electectronegative that the carbon atom.
The presence of these permanent dipole allows for the formation of dipole-dipole attractions between chloromethane molecules
Are haloalkanes soluble in water
They are slightly more soluble than hydrocarbons in h2o. But the solubility is still very low because the overalll influence of the dipole dipole interaction is small.
What happens to solubility of haloalkane as carbon chain length increases
The influence of the halogen decreases as the carbon chain length increases, haloalkanes become less soluble in h2o with increasing chain length as non polar character increases
Are haloalkanes more dense that h2o
They are denser than h2o and settle to form a layer at the bottom when added to water when it is insoluble or saturated
Which homologous series can form hydrogen bonds
alcohol, carboxylic acids, amines, amides
Compare intermolecular forces of alcohols and carboxylic acids
There is no dimerisation between alcohols. Therefore H bonding gin alcohols is weaker than carboxylic acids. strong H bonds due to dimerisation
Explain why carboxylic acids may not be a good fuel compared to alcohols (compounds have similar molar masses)
Alcohols are a better fuel than carboxylic acids. Carboxylic acids dimerise, therefore their H bondings are stronger, flashpoint is higher. Alcohols do not dimerise hence weaker H bonding, lower flashpoint. The lower the flashpoint, the fuel which has this will be a better fuel.
Why are haloalkanes and amines not used as fuels
Upon combustion of haloalkanes they release halo oxides while amides release toxic oxides of nitrogen.
Explain the intermolecular bonding in amines
-Nitrogen is less electronegative compared to oxygen. Therefore H bonding in amines is weaker than alcohol and weaker than amides
Explain the intermolcular bonding in amides
- More number of hydrogen bonds between amide molecules forming
- H bonds produced by oxygen will be stronger due to higher electronegativity
Explain the solubility in water of an alcohol
- H bonding between water and alcohol means it readily dissolves in water
- Longer the R group in the alcohol, it has more non polar characteristics therefore solubility in water decreases
Explain solubility in water of amines
Due to less electronegativity of H, H bonding forms with water, weaker than that of an alcohol
`Explain solubility in water of acids
Acids ionise in water as a result of ionisation they produce RCOO- and H3O+ so ionic interactions form when dissolved in water
Which homologous series only form dipole dipole and dispersion
Aldehydes, keytones and esters
Which fuel is better, methane or fluoromethane?
Methane: non polar, intermolecular forces are dispersion only, lower flashpoint, product of complete combustion is Co2 and h2O
Fluoromethane: polar, intermolecular forces are dipole-dipole and dispersion, higher flashpoint, products of combustion are co2 h2o and fluorooxides which is toxic.
therefore methane is a better fuel that fluoromethane
What is needed for a substituition reaction and why
Uv light is needed and it is and energy source to overcome Ea of substitution reaction
Alkene to alkane reaction
Needs Ni(catalyst). Breaks double bond
Alkene to alcohol
Needs h3PO4/300 degrees and requires a H2O molecule to break the bond and create an alcohol
Alkene to haloalkane
Needs X2 and the X goes on opposite sides of carbon atoms
What is needed to oxidise alcohols
Potassium dichromate (K2Cr2O7) and potassium permanganate (KMnO4)
Oxidising a primary alcohol
Aldehyde and if heated, carboxylic acid
Oxidation of secondary alcohols
Keytone is produced where the OH bond used to be
Why do tertiary alcohols not oxidise
During oxidation of alcohols there is an increase in the number of C-O bonds and a simultaneous decrease at the same carbon atom in the number of C-H bonds/ In tertiary alcohols the carbon attached to the hydroxy group does not have a C-H bond to break so oxidation cannot occur at that carbon atom.
Reaction of carboxylic acid with primary amide
primary amides can be prepared by the reaction of a carboxylic acid with ammonia. Condensation reaction
Reaction of carboxylic acid with primary amine
secondary amide plus h2o. Amide link is formed in this reaction
Markovnikov’s rule
The most electronegative functional group will be added to the carbon attached to the least number of H’s in a an addition reaction.
Of a cis and trans isomer which would have a higher melting point and why?
Tran would have a higher melting point as it isn able to pack more closely therefore stronger dispersion forces that require more heat energy to overcome. These override the relatively strong dipole dipole forced in the polar cis form (trans in non polar so dispersion forces only)
Of a cis and trans isomer which would have a higher boiling point and why?
Cis as it is a polar molecule. Therefore it has dipole dipole interactions between them that are stronger than the dispersion forces in the non polar trans form. In a liquid packing of the molecules has no effect. dipole dipole forces require more heat energy to break than the dispersion forces.
Order or priority for naming organic compounds
- carboxyl
- hydroxyl
- Amino
- double or triple carbon bonds
- halogens and alkyl branches (equal)
