Unit 2 Flashcards
Nucleophiles
Nucleophiles are negatively charged ions or neutral molecules that are electron rich.
They are attracted towards atoms bearing a partial or full + charge.
They are capable of donating an electron pair to form a new covalent bond.
Nucleophiles are nucleus loving and so nucleophiles are attracted and will attack species with a + charge.
Electrophiles
Electrophiles are positively charged ions or neutral molecules that are deficient in electrons.
They are attracted towards atoms bearing a partial or full - charge.
They are capable of accepting an electron pair to form a new covalent bond.
Electrophiles are electron loving and so Electrophiles are attracted and will attack species with a - charge.
2 types of stereoisomer
Geometric
Optical
Geometric isomers
Arise due to a lack of free rotation around a bond, frequently C=C, but not always.
Must have 2 different groups attached to each of the C atoms.
Non-superimposable
Cis isomer
The 2 largest groups are on the same side
Trans isomer
The 2 largest groups are on opposite sides.
Optical isomers
Arise as they have a chiral centre
They are asymmetric, non-superimposable mirror images of each other.
Chiral
4 different groups arranged tetrahedrally around a central carbon atom.
Enantiomers
Optical isomers can be described as enantiomers.
They have identical physical and chemical properties except :
Their effect on plane polarised light
Their reaction with other chiral molecules
Racemic mix
Contains a 50/50 mix of 2 enantiomers.
This is optically inactive
How to differentiate between 2 optical isomers ?
Subject them to plane polarised light.
Each enantiomer will rotate the light by the same angle but in opposite directions.
Drugs
Substances that alter the biochemical processes in the body.
Medicine
A drug that has a beneficial impact on the body
What do medicines contain ?
They contain the drug and often have other added ingredients such as fillers to add bulk or sweeteners to improve taste.
Agonists
Agonists MIMIC the natural compound and bind to the receptor molecules to produce a similar response to it.
The drug form ionic bonds with the receptor.
Antagonists
Antagonists prevent the natural compound from binding, and so blocks the natural response from occurring.
Enzyme inhibitors
Drugs that act on enzymes are classed as enzyme inhibitors and act by binding to the active site of the enzyme. This blocks the reaction normally catalysed here.
Pharmacophore
The structural fragment of a drug molecule that allows it to form interactions with a receptor.
Experimental determination of structure
Elemental microanalysis
Mass spectroscopy
Infrared spectroscopy
NMR spectroscopy
Elemental microanalysis
Used to determine the masses of C, H, O, S and N in a sample of an organic compound, in order to determine its empirical formula.
Empirical formula
The simplest ratio of elements in a substance/ molecule.
Mass spectroscopy
Used to determine the accurate GFM and structural features of an organic compound.
Infrared Spectroscopy
Used to determine and identify certain functional groups in an organic compound.
NMR Spectroscopy
Gives information about different chemical environments of H atoms in an organic compound. Allows recognition of how many H atoms are in each environment.
Molecular Orbitals
Molecular orbitals are generated when atomic orbitals combine.
The number of molecular orbitals formed is always equal to the number of atomic orbitals that combine.
Sigma bond
Molecular orbitals overlap end on.
Single bonds are sigma bonds.
Pi bond
Molecular orbitals overlap side on.
Double bonds contain 1 pi bond and 1 sigma bond.
Triple bonds contain 2 pi bonds and 1 sigma bond.
Pi bond V sigma bond
Pi bonds are weaker than sigma bonds
Hybridisation
Hybridisation is the process of mixing atomic orbitals within an atom, to form a set of new atomic orbitals called hybrid orbitals. These hybrid orbitals are degenerate.
sp3 hybridisation
Found in alkANES
Only have sigma bonds.
sp2 hybridisation
Found in alkENES
Have sigma and pi bonds.
sp hybridisation
Found in alkYNES
Has 2 pi bonds and 1 sigma bond.
HOMO
The orbital containing electrons with the highest energy is known as the Highest Occupied Molecular Orbital.
LUMO
The lowest energy anti-bonding orbital which is vacant is called the Lowest Unoccupied Molecular Orbital.
Chromophore
A group of atoms within a molecule responsible for the absorption of light in the visible region of the spectrum.
Conjugation
Alternating single and double carbon to carbon bonds.
Reaction of haloalkanes
Elimination : to produce an alkene
Nucleophilic Substitution : to produce an ( alcohol, nitrile OR ether )
How are haloalkanes classified ?
Haloalkanes are classified according to the number of alkyl groups (R) attached to the carbon containing the halogen atom.
Haloalkanes
Haloalkanes are substituted alkanes in which one or more hydrogen atoms are replaced by a halogen atom.
3 types of monohaloalkanes
Primary
Secondary
Tertiary
Haloalkane Elimination
Monohaloalkane + NaOH (eth) ——————————> Alkene
Note : The OH- removes a H atom from a C atom adjacent to the halogen. The halogen is
ejected.
Haloalkanes Nucleophilic Substitution reactions
Monohaloalkane + NaOH (aq) ——————————> Alcohol
Monohaloalkane + NaCN (eth) ——————————> Nitrile
Monohaloalkane + Alcoholic Alkoxide ——————————> Ether
Note : Alkali metal + Alcohol ——————————> Alcoholic Alkoxide
Mechanisms of nucleophilic substitution reactions
2 types of mechanisms :
SN1
SN2
SN1
1st order with respect to the haloalkane
One molecule involved in the slowest step
Tertiary haloalkanes usually undergo SN1
A Trigonal planar CARBOCATION intermediate is formed.
What is formed in the SN1 mechanism ?
A Trigonal planar carbocation intermediate, stabilised by the inductive effect from the CH3 groups.
SN2 mechanism
2nd order
2 molecules involved in the slowest step
Primary haloalkanes usually undergo SN2
Proceeds via a 5 centred ( Trigonal bipyramidal ) transition state.
What does the SN2 mechanism proceed by ?
Via a 5 centred Trigonal bipyramidal transition state
Alcohols
Alcohols are substituted alkanes, where one or more of the H atoms is replaced with a hydroxyl functional group.
Preparation of alcohols
Nucleophilic Substitution
Hydration / Addition
Reduction
Monohaloalkane + NaOH (aq) ———————————-> alcohol
conc. H2SO4 Alkene + water ———————————-> alcohol
Aldehyde/Ketone + LiAlH4 ———————————-> alcohol
Reactions of Alcohols
Oxidation (using acidified permanganate)
Dehydration (using conc. H2SO4)
Condensation / Esterification (using conc. H2SO4)
Primary alcohol ———————————-> aldehyde
Secondary alcohol ———————————-> ketone
Alcohol ———————————-> alkene
Alcohol + Carboxylic acid ———————————-> ester
Physical properties of alcohols
Hydroxyl group gives rise to H bonding
H bonding results in a higher boiling point
The polar -OH group allows alcohols to be miscible in water.
As the C chain increases, solubility decreases.
Ethers
Ethers are substituted alkanes in which a H-atom is replaced with an alkoxy functional group.
R’ ——O—— R”
Naming ethers
The smaller R—O is given a position and ends in oxy
E.g. methoxy
ethoxy
propoxy etc.
The longest chain is named after an alkane.
E.g. methane
ethane
propane Etc.
Preparation of ethers
Nucleophilic substitution
Monohaloalkane + alcoholic alkoxide ———————————-> ether
Properties of ethers
Due to a lack of H bonding, ethers have a lower boiling point than the corresponding isomeric alcohols.
Large ethers are INSOLUBLE in water due to increased molecular size.
Uses of ethers
Ethers are commonly used as SOLVENTS; since they are relatively INERT chemically and dissolve easily.
Preparation of Alkenes
Elimination reaction
Dehydration of an alcohol
Monohaloalkane + NaOH(eth) ———————————-> alkene
alcohol ———————————-> alkene + H2O
What process do Alkenes react by ?
Electrophilic Addition
Reactions of Alkenes
Hydrogen + alkene ———————————-> alkane
Halogen + alkene ———————————-> dihaloalkane
Hydrogen Halide + alkene ———————————-> monohaloalkane
Water + alkene (acid catalyst) ———————————-> alcohol
Markovnikovs Rule
Used to determine which of 2 products is in greater yield.
The major product is the one in which the H atom attaches to the C of the double bond that has the greater number of Hs bonded to it.
Preparation of Carboxylic acids
Oxidation of primary alcohols (using XS acidified dichromate) / aldehydes (using acidified dichromate)
Hydrolysis of ( nitriles, esters or amides ) using an aqueous alkali
Nitrile
Ester + H2O ——————————> Carboxylic acid
Amide
Reactions of Carboxylic acids
Carboxylic acid
+ metal/base ———————-> salt
+ alcohol ( conc. H2SO4 ) ———————-> ester
+ amine ———————-> alkyl-ammonium salt
+ LiAlH4 ———————-> primary alcohol
Amines
Amines are organic derivatives of ammonia, in which one or more H atoms are replaced by an alkyl group.
How are amines classified ?
Classified according to the number of alkyl groups attached to the nitrogen atom.
Can be classed as :
Primary
Secondary
Tertiary
Physical properties of amines
Primary and secondary amines contain a polar N—H bond and so display H bonding.
As a result, they have higher bpts than isomeric tertiary amines.
Tertiary amines do not display H bonding
All 3 can H-bond with water, thus explaining the appreciable solubility of the shorter chain length amines in water.
Reactions of Amines
Amine + acid ———————-> alkyl-ammonium salt
Alkyl ammonium salt + HEAT ———————-> amide
Benzene
C6H6
The simplest member of the class of aromatic hydrocarbons
How are benzene rings stable ?
The stability of the benzene ring is due to the delocalisation of electrons in the conjugated system.
What method does benzene react by ?
Electrophilic SUBSTITUTION
The H/ Hs are replaced by atoms or groups (the electrophiles)
Phenyl group
A benzene ring in which one H atom has been substituted by another group (known as a phenyl group) C6H5
Reactions of benzene
Alkylation
Sulfonation
Halogenation
Nitration
Alkylation
Benzene + AlCl3 + R-Cl ———————-> alkylbenzene
Halogenation
Benzene + AlCl3 + X2 ———————-> halobenzene
Sulfonation
Benzene + conc. H2SO4 ———————-> benzenesulfonic acid
Nitration
Benzene + conc. H2SO4 + HNO3 ———————-> nitrobenzene
Bond fission
The process of bond breaking is known as bond fission.
A bond can break in 2 ways :
Homolytic fission
Heterolytic fission
Homolytic fission
Occurs when non-polar covalent bonds are broken.
Free radicals are produced.
Caused by HIGH ENERGY UV light.
Can produce multiple undesirable products.
Heterolytic Fission
Occurs when polar covalent bonds are broken.
Ions are produced.
Double headed arrows are used.
Results in far fewer products than Homolytic fission, and as a result are better suited in the synthesis of organic compounds.
sp3 hybridisation
One s atomic orbital mixes with three p atomic orbitals to form 4 hybrid orbitals, which are degenerate.
sp2 hybridisation
One s atomic orbital mixes with two p atomic orbitals to form 3 hybrid orbitals, which are degenerate.
The remaining p orbital is left unhybridised.
sp hybridisation
One s atomic orbital mixes with one p atomic orbitals to form 2 hybrid orbitals, which are degenerate.
The remaining two p orbitals are left unhybridised.
