An Introduction to A-Level Organic Chemistry Flashcards
Aromatic compounds
-molecules that consist of one or more rings with conjugated π systems
-are called ‘aromatic’ as they often have pleasant odours
Conjugated π systems
arise from alternating double and single bonds in which the electrons are delocalised
Functional group
an atom or group of atoms in an organic molecule, that determines its characteristic chemical and physical properties
Arenes
aromatic compounds that contain a benzene ring
Chemical properties of arenes
-Due to the delocalised electron ring, arenes are electron-rich and therefore can undergo electrophilic attack under the right conditions.
-However the delocalised electron ring system also makes benzene so stable to the extent that it is resistant to addition reactions, thus they are different to alkenes, which are very reactive and readily undergo addition reactions
Physical properties of arenes
b.p, IMF, solubility
-Benzene has van der Waals dispersion forces of attraction between the molecules and has a boiling point of 80 C
-Because of the presence of the non-polar hydrocarbon part in the arene functional group, these compounds are often insoluble in water
-Benzene isn’t soluble in water because it would have to break many hydrogen bonds between the water molecules to dissolve which doesn’t happen because it isn’t energetically favourable
Halogenoarenes
aromatic compounds that contain a halogen bonded to a benzene ring
Another name for halogenoarenes
aryl halides
Chemical properties of halogenoarenes
-compounds prone to electrophilic attack because of the π system of delocalised electrons
-the halogens can also take part in substitution reactions
Physical properties of halogenoarenes
condition at r.t.p, b.p, solubility
-Chlorobenzene, bromobenzene and iodobenzene are all liquid at room temperature with an oily texture
-The boiling points increase as the size of the halogen attached increases because the number of electrons within the molecule increases
-Insoluble in water because of the non-polar hydrocarbon part of the ring
-Molecules are large relative to the size of water molecules, and it is not energetically favourable for the halogenoarene molecules to break the hydrogen bonds between the water molecules in order to dissolve
Phenols
a type of aromatic compounds containing a hydroxide bonded to a benzene ring
Chemical properties of phenols
acidity, reactivity, reactions
-The -OH group in phenols is more acidic than in alcohols as the oxygen donates one of its lone pairs of electrons into the ring system
-This causes an increased electron density of the ring, causing it to become much more reactive than benzene itself
-It also makes it easier for the hydrogen of the -OH group to be donated
-Phenols can also react with reactive metals such as sodium to form alkoxide ions
Physical properties of phenols
-Phenol is a white, crystalline solid, and it has a disinfectant-like smell
-Due to the -OH group in phenols, they can form hydrogen bonds with water molecules, and therefore to a degree phenol is soluble in water
Acyl chlorides
carboxylic acid derivatives containing:
-A chlorine atom attached to a C=O group (replacing what would have been the -OH group of a carboxylic acid)
-An acyl (hydrocarbon) group attached to a C=O group
Another name for acyl chlorides
acid chlorides
Chemical properties of acyl chlorides
-They are fuming liquids and are colourless, with a strong smell
-Acyl chlorides are extremely reactive and readily take part in substitution reactions in which the chlorine atom is substituted by other species
-This reactivity is why they are fuming liquids and why they have such a strong smell - they react with any water vapour in the air
Physical properties of acyl chlorides
Acyl chlorides react violently with water, so we cannot say whether or not they would be soluble in water
Amines
compounds with the -NH2 (primary amine), -NH (secondary amine) or -N (tertiary amine) group
Classification of amines
-In primary amines, the N of the amine group is bonded to one R group (and two hydrogen atoms)
-In secondary amines, the N of the amine group is bonded to two R groups (and one hydrogen atom)
-In tertiary amines, the N of the amine group is bonded to three R groups
Chemical properties of amines
Due to the lone pair of electrons on the nitrogen, amines are basic compounds
Physical properties of amines
-The lone pair on the N of the amine group means that they can form hydrogen bonds
-They are often soluble in water because they form hydrogen bonds with water molecules
-The smaller amines are very soluble in water, but their solubility decreases as the non-polar hydrocarbon chain gets longer
-They often have a fishy smell, especially as the size of the amines increases
Amides
compounds containing:
-An amine (-NH2) group
-A carbonyl group (C=O)
The amide group is -CONH2
Chemical properties of amides
Amides are less basic than amines, as the lone pair of electrons on the nitrogen is delocalised
Physical properties of amides
-Amides are often soluble in water as they can form hydrogen bonds with water molecules
-The smaller amides are very soluble in water, but their solubility decreases as the non-polar hydrocarbon chain gets longer
Amino acids
building blocks of proteins and consists of:
-An amine (-NH2) group
-A carboxyl (-COOH) group
Chemical properties of amino acids
-react with bases to form salts
-react with alcohols to form esters
-react with amines to gives amides
Physical properties of amino acids
-soluble in water but insoluble in organic solvents
-have chiral centres and exhibit optical isomers (except for glycine)
General Formula of Arenes
CnH2n-6M
n=number of C atoms m=number of rings
General Formula of Halogenoarenes
CnH2n-7mX
General Formula of Phenols
CnH2n-7mOH
General Formula of Acyl Chlorides
RCOCl
General Formula of Amines
CnH2n+3N
General Formula of Amides
RCONH2
General Formula of Amino Acids
HOOCCHRNH2
naming organic compounds: aliphatic compounds
1)Identify the longest carbon chain containing the functional group
2)Identify the functional group on the chain to determine the suffix or prefix on the compound
3)Count along the carbon chain such that the functional group has the lowest number
4)Add any side chains or lower priority functional groups as prefixes to the beginning of the name in alphabetic order
5)Use the prefixes di-, tri- and tetra- if there are two or more identical functional groups or side chains
Electrophiles
‘electron loving’ species that are electron deficient and can act as an electron pair acceptor
Substitution reactions
reactions that involve the replacement of one atom or group of atoms by another
Electrophilic substitution reactions
reactions in which an atom or group of atoms are replaced by an electrophile after initial attack by the electron-deficient species
Addition reactions
reactions in which two or more molecules combine to give a single product only
Elimination reactions
the reverse of addition reactions; a small molecule (such as H2O or HCl) is removed or ‘eliminated’ from an organic molecule
The shape of benzene & aromatic compounds
-contain sp2 hybridised carbons as two of their p orbitals have mixed with an s orbital
-each carbon atom in the ring forms three σ bonds using the sp2 orbitals
-remaining p orbital overlaps laterally with p orbitals of neighbouring carbon atoms to form a π bond resulting in the electrons being delocalised and being able to spread over the entire ring freely
-are regular and planar compounds with bond angles of 120 degrees
-delocalisation of electrons means that all of the carbon-carbon bonds in these compounds are identical and have both single and double bond characters; bonds are all the same length
Stereoisomers
are molecules that have the same structural formula but have the atoms arranged differently in space
Two types of stereoisomers
Geometrical (cis/trans) and Optical
Optical isomerism
A carbon atom that has four different atoms or groups of atoms attached to it is called a chiral carbon or chiral centre
enantiomers
optical isomers that are mirror images of each other and are non-superimposable
similarities and differences between enantiomers
-their physical and chemical properties are identical
-differ in their ability to rotate plane polarised light
-differ from each other in terms of their biological activity
Biological activity of enantiomers
-Enzymes are chiral proteins that speed up chemical reactions by binding substrates
-They are very target-specific as they have a specific binding site and will only bind molecules that have the exact same shape
-Therefore, if one enantiomer binds to a chiral enzyme, the mirror image of this enantiomer will not bind nearly as well if at all
optically active mixture
-When a solution contains an uneven mixture of each enantiomer
-For example, 20% of a solution contains an enantiomer that rotates the plane of polarised light clockwise and 80% of the solution has an enantiomer that rotates the plane of polarised light anticlockwise; the net effect is that the plane of polarised light will be rotated anticlockwise
racemic mixture
a mixture in which there are equal amounts of enantiomers present in the solution so plane polarised light remains unchanged
R enantiomer
the enantiomer that rotates the plane polarised light clockwise
S enantiomer
the enantiomer that rotates the plane polarised light anticlockwise
How can the identity of an optical isomer of a single substance be identified?
using the rotation of plane-polarised light, depending on which isomer the sample contains, the plane of polarised light will be rotated either clockwise or anti-clockwise
Why is it important that only one enantiomer of the optical isomer be produced when manufacturing drugs
-to increase the drugs’ effectiveness
-to avoid drug enantiomers that have very harmful side effects
What happens when conventional organic reactions are used to make the desired drug
a racemic mixture will be obtained
examples of drug chirality affecting its effectiveness
-the drug naproxen is used to treat pain in patients that suffer from arthritis; one of the enantiomers of naproxen eases the pain while the other enantiomer causes liver damage
-one enantiomer of a drug used to treat tuberculosis is effective whereas another enantiomer of this drug can cause blindness
-thalidomide is another example of a drug that used to be used to treat morning sickness, where one of the enantiomers caused very harmful side effects for the unborn baby
Why it’s very important to separate a racemic mixture into pure single enantiomers when they are being put in the drug product
- reduced side effects in patients; it protects pharmaceutical companies from legal actions if the side effects are too serious
-decreases the patient’s dosage by half as the pure enantiomer is more potent and therefore reduces production costs; a more potent drug has a better therapeutic activity
What should be used in order to produce single, pure optical isomers
chiral catalysts
benefits of using chiral catalysts
only small amounts of them are needed and they can be reused
why are enzymes excellent biological chiral catalysts
they promote stereoselectivity and produce single-enantiomer products only
Stereoselectivity
refers to the preference of a reaction to form one enantiomer over the other
How enzymes help in promoting stereoselectivity and produce single-enantiomer products only
-Due to the specific binding site of enzymes, only one enantiomer is formed in the reaction
-The enzymes are fixed in place on inert supports so that the reactants can pass over them without having to later separate the product from the enzymes
the disadvantages of using enzymes to produce single-enantiomer products only and how to counterattack it
-it can be expensive to isolate them from living organisms; therefore, more research has recently been carried out into designing synthetic enzymes
-using enzymes takes longer than conventional synthetic routes however using enzymes is also a greener process as fewer steps are involved compared to conventional synthetic routes
