introduction to organic chemistry

HYDROCARBON - are organic compounds that contain carbon and hydrogen only 

SATURATED HYDROCARBON - is a hydrocarbon with with single bonds 

UNSATURATED HYDROCARBON - conatins carbon-to-carbon multiple bonds

ALIPHATIC  HYDROCARBON - a carbon atoms joined together or in brached chains 

ALICYLIC HYDROCARBONS - carbon atoms joined together in a ring structure 

Methods

Chemical reactions occur at a definite rate determined by the reaction conditions. The rate of reaction may be increased by:

1. Increasing temperature
2. Increasing concentration of reactants
3. Increasing surface area

Many reactions are subject to kinetic control.

Collision theory 

• Only those molecules having energy above a certain minimum value will react when they collide

• This minimum energy value is called the activation energy

• The activation energy can be thought of as anenergy barrier to the progress of the reaction.

Energy-profile diagrams:

• The rate of reaction is directly related to the size of the activation energy.

The spread of energies in a sample of gas molecules is given by the Maxwell-Boltzmann distribution curve. Frequent collisions between molecules results in a spread of high and low energy molecules.

• At the lower temperature T1, the number of molecules with energy greater than activation energy is given by the purple shaded area. 

• An increase in temperature to T2 results in a large increase in the number of such molecules.

• This increase is represented by the light blue shaded area.

• Therefore, the number of 'productive collisions' will be much greater at higher temperatures and so the rate will not be much 

This is a high energy species in which old bonds are partially broken and new bonds are partially formed.

Mechanism

• A catalyst speeds up a chemical reaction without itself undergoing any permanent chemical change.

• They are usually specific to one particular reaction and they speed up both forward and back reactions equally.

• All types of catalyst work by providing an alternative pathway that has a lower activation energy than the original one.

In the presence of a catalyst a new pathway is created.

Homogenous catalysis

Homogenous catalysts function in the same state as the reactants (usually all in aqueous solution).

Example:

CH₃COOH_(aq) + C₂H₅OH_(aq) → CH₃COOC₂H_5(aq) + H₂O_(l) is catalysed by the acid: H⁺_(aq)

Enzymes are important homogenous catalysts.

An instrument called a mass spectrometer is used to calculate relative atomic mass.

In a mass spectrometer:

• atoms are converted to positive ions; 
•  then deflected by electric and magnetic fields before being detected.
•  The mass of the elements individual isotopes are found as well as their abundance.
• 
  

From this data the Relative Atomic Mass can be found.

Equilibrium of reactions

 Mechanism of bond breaking and making

A covalent bond can be broken in two ways:

a) Homolytic fission

• A:B → A^o + B^o

Produces free radicals which have an unpaired electron and are very reactive.

 Heterolytic fission

• A:B → A⁺ + B^-
• A:B → A^- + B⁺

Produces ions.

dipoles come about when there is unequal distrubution between electronsin the molecule because some  tend to attractor repel electrons 

Chlorine has a greater share of the electrons due to the electronegativity it possesses:

Groups which are attracting electrons have a negative inductive (-I) effect. They give rise to electron deficient atoms C^δ+.

Groups which are electron repelling have a positive inductive (+I) effect. They give rise to electron rich carbon atoms C^δ-.

Nucleophiles: Attack centres of low electron density (nucleus loving). They possess a lone pair of electrons and are usually negatively charged.

Examples include: H₂O, ROH, OH^-, RO^-, Br^-, NH₃, RNH₂, CN^-.

Electrophiles: Attack centres of high electron density (electron loving) The are capable of accepting a lone pair of electrons and are usually positively charged.

Examples include: H⁺, Br⁺, R-N=N, CN^-.

FUNCTIONAL GROUP - the part of the organic molecule resposible for its reactions 

molecules with same functional group react in a similar way 

 HOMOLOUS SERIES- series of compound with same functional group but with each successive member differing by CH2

ALKANES-are homologous series with the general formula  C_nH_2n+2 

 addition polymerisation, alkenes add to themselves. 

The alkene is the repeating unit