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Organic Chemistry | Topic Notes^1
Organic Chemistry | Topic Notes
- Organic chemistry is the study of^ compounds of carbon.
- A functional group is an atom or group of atoms which is responsible for the characteristic properties of a series of organic compounds.
Organic Chemistry Table
Homologous Series Functional Group Structure of Group
Name Example
Alkane Single bond - Propane Alkene Double bond !Unexpected End of Formula
Propene
Alkyne Triple bond ≡^ Propyne Chloroalkane H’s replaced by Cl’s - Cl Chloropropane
Alcohol Hydroxyl - OH Propanol Aldehyde Carbonyl (end) - C=O(H) Propanal Ketone Carbonyl (middle) - C=O Propanone Carboxylic Acid Carboxyl - C=OOH Propanoic Acid Ester Bridging oxygen - COO- Methyl ethanoate
Hydrocarbons: Compounds that contain carbon and hydrogen only.
Saturated: Contain only single bonds.
Homologous Series: A series of compounds of uniform chemical type, showing graduation in physical properties with a general formula for it’s members. They have a similar method of preparation.
Prefix No. of Carbons Meth - 1 Eth - 2 Prop - 3 But - 4 Pent - 5 Hex - 6 Hept - 7 Oct - 8 Non - 9 Dec - 10
Mike Eats Pringles But Prefers Hula Hoops On Nasty Days.
Organic Chemistry | Topic Notes^5
Alkanes
- Shape: tetrahedral - never planar.
- Bonds: All single bonds - saturated.
- General Formula: CNH2N+
- Ending: -ane (eg: propane)
CH4 - Methane C2H6 - Ethane C3H8 - Propane
H H H H H H | | | | | | H -- C -- H H -- C -- C -- H H -- C -- C -- C -- H | | | | | | H H H H H H
- Carbon Carbon single bonds. C---C functional group
- They are saturated. This means that they undergo substitution reactions. This will be described later (free radical substitution and saponification).
- Meth^ -^ ane
- Eth^ -^ ane
- Prop^ -^ ane
- But^ -^ ane
- Pentane^ -^ ane
- Hex^ -^ ane
- Hept^ -^ ane
Organic Chemistry | Topic Notes^7
Alcohols
A homologous series similar to alkanes but with a hydrogen replaced by an -OH (hydroxyl) group. The ending is -anol (eg: propanol). The general formula is CNH2N+1OH.
There are primary, secondary and tertiary alcohols. Primary alcohols are when the carbon attached to the hydroxyl group touches one other carbon. Secondary alcohols are when the carbon attached to the hydroxyl group touches two other carbons. Tertiary alcohols are when the carbon attached to the hydroxyl group touches three other carbon.
*Always indicate the position of the hydroxyl group when naming alcohols. For example 2methylbutan-1-ol which has a methyl group attached to the second carbon and the hydroxyl group is attached to the first carbon.
The hydroxyl group of the alcohols changes their chemistry drastically from their corresponding alkanes. In particular, it affects their boiling points and solubility.
Boiling Points
The hydroxyl group (-OH) undergoes hydrogen bonding, resulting in them having very strong bonds. As a result, their boiling points are higher than those of the corresponding alkanes as it takes more energy to break apart the bonds.
Solubility The solubility changes as the length of the carbon chain increases. The OH group is highly polar and if the chain is short it forces the non-polar carbon chain to dissolve in polar substances such as water. If the chain becomes too long the OH group can no longer force the chain to dissolve in polar substances so it dissolves in non-polar substances instead (cyclohexane). (Like dissolves like.)
- -OH^ is the functional group. Called the Hydroxyl group.
- Remember - alc OH ol
- General formula is CnH2n+1OH (alkyl + OH group)
- The -OH group is V shaped and the shape around each carbon atom is tetrahedral.
- Alcohols are named by replacing the -ane from its corresponding alkane with^ -anol
- Primary Alcohol -^ Where the carbon atom joined to the -OH group is attached to only ONE other carbon atom. e.g. Ethanol & Methanol.
- Secondary Alcohol -^ Where the carbon atom joined to the -OH group is joined to TWO other carbon atoms. e.g. propan-2-ol
- Tertiary Alcohol -^ Where the carbon atom joined to the -OH group is joined to THREE other carbon atoms. e.g. 2methylpropan-2-ol.
Chloroalkanes
- An alkane with one or more of it’s hydrogens replaced by chlorines.
- Shape: tetrahedral - never planar.
- Bonds: All single bonds - saturated.
- Ending: Chloro-ane (eg: chloropropane)
- If there are two chlorines it’s di-chloro-ane, if there are three chlorines it’s tri-chloro- ane, if there are four chlorines it’s tetra-chloro-ane.
CH3Cl - Chloromethane C3H5Cl3 - 1,1,2-triChloropropane
Cl H Cl H H Cl | | | | | | H -- C -- H H -- C -- C -- H H -- C -- C -- C -- Cl | | | | | | H H Cl H Cl H
C2H4Cl2 - 1,1-diChloroethane
- Chloroalkanes are compounds in which one or more of the hydrogen atoms in an alkane molecule have been replaced by a chlorine atom.
Organic Chemistry | Topic Notes^11
- They are mainly used for removing oil and grease marks from machinery, in dry cleaning and chloroform was used as an anaesthetic.
- They aren’t soluble in water but are soluble in non polar^ solvents such as cyclohexane. They also have low boiling points.
- Rarely found naturally occuring.
Organic Chemistry | Topic Notes^13
H H H H H H H H H
- Contain Carbon Carbon double bonds.
- They are unsaturated which means they under go addition reactions.
- Replace -ane with -ene
- Only need to know Ethene, Propene, Butene.
- Ethene is the starting material from which many substances are made. e.g. Polythene, PVC, Polystyrene, synthetic rubber etc...Also used to ripen fruit commercially.
- Note: Ethene is prepared by dehydrating ethanol, a primary alcohol. The dehydrating agent is Aluminium oxide. This is explained later.
Alkynes
- Shape: both tetrahedral and planar - tetrahedral everywhere but where the triple bond is.
- Bonds: Unsaturated - contains a triple bond.
- General Formula: CNH2N-
- Ending: -yne (eg: propyne)
C3H4 - Propyne C4H6 - Butyne
H H H
H -- C ≡ C -- C -- H H -- C ≡ C -- C -- C -- H
H H H
- Contain carbon carbon triple bonds and are highly unsaturated.
- Replace -ane with -yne
- Ethyne or Acetylene is used as Oxyacetylene in fire extinguishers, welding and cutting.
- Water and calcium carbide form ethyne, however bubble through copper sulfate solution to get rid of impurities like phosphine, ammonia and hydrogen sulfide gas.
The first few aldehydes and ketones are soluble in water (polar) and the rest are soluble in cyclohexane (non-polar) as the dipole-dipole forces can only force a few carbons to dissolve in a polar substance.
- Functional group is -CHO where C and O is a double bond.
- General formula is RCHO
- Aliphatic Aldehydes are CnH2n+1CHO.
- -ane is replaced by -anal.
- Remember; methanal, propanal, ethanal and butanal or 2-methylpropanal.
- The C = O group or Carbonyl group is highly polar. This means that compounds containing a carbonyl group cannot for hydrogen bonds.
- The^ boiling points of Aldehydes are higher than the corresponding alkane because there are dipole dipole forces between aldehyde molecules.
- The^ boiling point of Aldehydes are lower than their corresponding alcohol because of the lack of hydrogen bonding between aldehyde molecules.
- Solubility of aldehydes decreases as the length of the carbon chain increases^ due to the portion of the insoluble alkyl molecules.
- Lower members of aldehydes are highly soluble^ in water^ because the O of the carbonyl group can form a hydrogen bond with the H of the water molecule.
- Most aldehydes are liquid at room temperature but methanal is gas.
- All aldehydes are quite soluble in organic solvents.
- Methanal in water is called^ Formalin^ and is used as embalming fluid and to preserve biological specimens.
Organic Chemistry | Topic Notes^17
- Benzaldehyde^ is found in the oil of almonds.
- They reduce Cu2+ ions to Cu+ ions, goes from blue to brick red in Fehlings Solution. (Fehling’s A = copper sulfate in water and Fehling’s B = potassium sodium tartrate)
- They reduce silver ions in dilute ammonia to silver metal
Organic Chemistry | Topic Notes^19
- Functional group -COOH
- General formula is RCOOH
- C=O and C-OH bonds.
- change the e in ane^ - - - oic
- Methanoic acid - stings of nettles and ants,
- Ethanoic acid - vinegar, cellulose acetate (photographic film and lacquers)
- Propanoic, benzoic and some of their salts preserve foods
- Butanoic acids - unwashed socks
- Decanoic acid - stench of goats.
- Hydrogen bonding can occur between molecules of carboxylic acids. They have a higher boiling point than their corresponding alcohol due to there being more hydrogen bonding between molecules.
- Lower members are highly soluble in water due to the carboxylic acid group forming hydrogen bonds with water molecule.
- The solubility of carboxylic acids decreases with length of carbon chain due to the insoluble alkyl portion of the molecule.
- Quite soluble in organic solvents.
- Pure ethanoic acid is liquid at room temperature but if it falls below 17 degrees it becomes solid. Glacial acetic acid is ethanoic acid when solid because of increased hydrogen bonding and clusters of Dimers (groups of 2 molecules joined together) held together by H bonding.
Esters
- -COO- functional group
- RCOOR’ general formula
- Derived from carboxylic acids by replacing H of OH group with an alkyl group.
- replace e in -ane with -oate
- Formed by reaction of alcohol and carboxylic acid. - condensation reaction as it loses a water molecule.
- Take note of naming. Start with the alkyl group attached to the oxygen atom and THEN with the carboxylic acid, changing the -oic to -oate. e.g. methylethanoate
- Esters are volatile liquids with pleasant fruity smells
- Fats and oils are naturally occuring esters from alcohol (glycerol) and long chain fatty acids.
- Ethyl ethanoate is made by heating ethanol, glacial ethanoic acid and a few drops of concentrated sulfuric acid. It is used as a solvent in many glues.
- Low boiling points because hydrogen bonding is not possible between ester molecules.
- Lower members are soluble in water as they can form hydrogen bonds
- Solubility decreases as length of carbon chain increases due to insoluble alkyl portion.
- soluble in organic solvents.
Aromatic Compounds
- Contain a benzene ring structure in their molecules.
- All of the bonds in a benzene ring are identical and are intermediate between double and single bonds.
