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Organic Chemistry
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Organic ChemistryHydrocarbons: How to Draw Organic Molecules
Hydrocarbons
Framework of organic molecules
Covalent based molecules- Carbon + Hydrogen
Covalent Bonding
Carbon- tetravalent central atom- four bonds
Hydrogen- 1 bond
Shape of molecule- 3 Dimensional, Tetrahedral
Alkane- Single C-C bond
Alkene- Double C=C bond
Alkyne- Triple C≡C bond
HCs are nonpolar (hydrophobic)
C-C, C-H bonds are nonpolar
e.g. Petrol- low boiling point and flammable
Functional groups- contain O,N,S,P, etc…. – are added via Covalent Bonds- diverse chemical properties
- Heteroatoms: O,N,S,P etc…
Draw molecules accurately
1. X-ray crystallography shows- chain of carbon atoms is not linear but ‘ZIG-ZAG’
2. Remove hydrogen atoms (C-H bonds) attached to carbon
3. Omit ‘C’
Alkanes
Alkanes- ‘backbone’ of organic molecules
Alkanes consist only of carbon and hydrogen- contain single bond
Alkanes are referred to as SATURATED- single bonds only
o saturated hydrogen atoms- they have ‘absorbed’ as many hydrogen atoms as they possibly can
Physical properties of alkanes
Hydrocarbon family are Non-polar molecules – comprise C and H atoms – held together by covalent bonds
o Neither C nor H are electronegative to cause polarity within molecule
o Lack polarity- can participate in strongly dipolar/ ionic interactions – Lack ability to form H bonds
Can only experience Dispersion forces -low melting/ boiling points- little energy required to overcome these
forces
o As size of alkane increases- melting/ boiling increases- increase in dispersion forces, operating
between molecules
o Number of electrons increases- stronger dispersion forces
Solubility in water
Insoluble in water – lack electronegative atoms- unable to form H-bonds with water
Chemical properties of alkanes
, Alkanes formed with strong single covalent C-H and C-C bonds – large amount of energy required to break
these bonds
Alkanes are very stable and lack of reactivity
o bonds joining atoms of alkane are hard to break –
o react readily with other compounds
o undergo combustion readily
Shape of organic compounds
Carbon’s valency of four- enables organic compounds to possess variety of shapes
Straight chain- hydrocarbons comprise Carbon atoms which are joined together – form continuous chain
Branched chain- hydrocarbons comprise Carbon backbone which branches- form two separate chains
Cyclic rings- straight carbon backbone join together- form cyclic/ ring structure
o when ends of hydrocarbon chains join forming ring structure – carbons at two ends of chain must
satisfy their valency of 4
Alkenes and Alkynes
Alkenes and Alkynes- carbon-carbon double bond and carbon-carbon
triple bond
Unsaturated- hydrocarbon containing carbon-carbon double or triple
bonds
Trans functional group-
Cis functional group-
Causes conformational (shape) change
Double Bond
Double bond- formed when two pairs of electrons are shared by Two atoms
o One pair of electrons- occupy σ bonding orbital – form σ bond
o Second pair of electrons- occupy π bonding orbital- form π bond
Acts like reserve of valence electrons – contains two more electrons
o Single σ bond- holds two atoms together
o π bond in double bond- strengthen linkage between two atoms – can be dispensed with freeing up
two valence electrons- without disrupting link between two atoms
Double bonds can join atoms of any elements that have valency of ≥ 2
Alkenes- Physical properties
Alkenes are non-polar molecules- experience only dispersion forces
Lack electronegative atom – can’t form Hydrogen bond- insolubility in water
Presence of double bond makes alkene more chemically reactive than alkane
Alkynes
Alkyne- Hydrocarbon which has one or more pairs of carbon atoms joined by triple bond
High energy triple bond- give alkynes much lower
stability than alkanes- far greater reactivity
Important functional groups in biological
chemistry
, Alkyl – resemble alkane molecules but with H atom removed from terminal C atom – enable molecule to join
o e.g. Alkyl group formed from removal of H atom from Methane- Methyl group
o Symbol R – used to represent any alkyl group
o Chain length outweighs Hydrophilic nature of Hydroxyl group – disrupts H bonding in H2O too
greatly
Small alkyl groups don’t disrupt structure of H2O- compound is water-soluble
Large alkyl group disrupt structure of H2O- compound is water-insoluble
Alcohol
o General formula- ROH
o Hydroxyl group: -O-H- single covalent bond between Hydroxyl group’s oxygen
atom and Carbon atom
e.g. Glycerol – comprises three Hydroxyl groups attached to tree
carbon backbone
o Alcohols are polar molecules- electrons withdrawn towards highly electronegative oxygen atom-
distorting distribution of electrons throughout molecules- Molecule is polar
o Alcohol can form hydrogen bonds with Water and with each other- makes chain soluble in water
Phenol- alcohol phenol comprised benzene ring attached to Hydroxyl group
Ether
o General formula- ROR’
o Combination of alkyl group and oxygen atom- alkoxyl group – attaches to hydrocarbon chain via
single covalent bond- linking Oxygen atom of ether group with Carbon atom from chain
o Ethers comprise two alkyl groups linked by bridging oxygen atom
o Ethers can form Hydrogen bonds with water (but can’t form within ethers)- soluble in water
Carbonyl groups
Possess Oxygen atom joined to Carbon atom by double covalent bond
- Contains both electronegative oxygen atom and double
bond
- Induces polarisation and has ability to form hydrogen
bonds
- Double bond- reserve of electrons
Carboxylic acid
o General formula- RCOOH
o Carboxyl group has two components- carbonyl group and Hydroxyl group
o Carboxylic acid that possess long alkyl chains form- Fatty acids- saturated/ unsaturated
o Possess two electronegative oxygen atom – one which has hydrogen atom attached – Are able to
participate in Hydrogen Bonding
o In gaseous carboxylic acids- join together in pairs- form Dimer – 2 hydrogen bonds are formed
Stable association between neighbouring carboxylic acid molecules
Carboxylic Ester
o General formula- RCOOR’
o Formed from joining through chemical reaction of alcohol and carboxylic acid – Esterification
o Can’t form Hydrogen Bonding
e.g. Triacylglycerols- based on alcohol glycerol and possess three ester groups
Ketone- Carbonyl group is attached to two carbon atoms (often two alkyl
groups)
Aldehyde- Carbonyl group is attached to one carbon and hydrogen atom
Monosaccharides are building blocks for polysaccharides (Starch, Cellulose, Chitin…)
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