STPM Chemistry Form 6 – Introduction of Organic Reaction (Part 1)

by BerryBerryTeacher

in Berry Reference (Notes)

Organic reactions for STPM Form 6 Chemistry simply means chemical reactions which involves organic compounds. From it, you’ll learn about basic organic chemistry reaction types with focus on reaction types such as substitution reactions, elimination reactions and addition reactions. (Other common reaction types like pericyclic reactions, rearrangement reactions, photochemical reactions and the familiar redox reactions is not discussed.) This post, Part 1 of the Introduction to Organic Reactions for STPM Form 6 Chemistry by Berry Berry Easy will be focussed on types of organic reactions.

The basics of reaction mechanisms which describe in detail chemical processes, potential energy diagrams and reaction intermediates. Students typically will find reaction mechanisms difficult, will underestimate the difficulty of potential energy diagrams and find reaction intermediates incomprehensible. So pay full attention to what is being taught in class as this chapter is very important for you to gain subsequent knowledge.

[Tips: Many Berry Readers cannot link the reaction types to actual examples. For example, substitution reactions can include radical substitions. Elimination reactions can involve processes such as dehydration. While halogenation, hydration and hydrohalogenation are actually addition reactions. So while, it is important to know the characteristics of the reaction types, it is also important to know the examples. This will improve your understanding. Try and figure out which reactions are substitution, elimination or addition reactions. Mental exercises like this will help you.

When learning reaction mechanisms, make sure that you know its intermediate types. Check if it has free radicals, carbocations or carbanions. Don't just learn the steps in the mechanism.]

STPM Chemistry Form 6 Notes – Introduction of Organic Reaction (Part 1)

 

Crude Petroleum

 

Type of Reaction (bonds are broken in the reactants and new bonds are formed in the products):

  • Substitution reaction – reaction that an atom or group on a molecule is replaced by another atom or group.
  • Elimination reaction – reaction that atoms or groups are removed from adjacent atoms to formed a double or triple bond.
  • Addition reaction – reaction that atoms or groups add to adjacent atoms of a multiple bond.

Reaction Mechanisms (description of how the reaction occurs):

  • Determine the number of steps involve in a reaction – one-step mechanism / two-step mechanisms
  • Determine any short-lived intermediate species formed during the steps of the reaction.
  • Determine charged or neutral species involved.

Potential Energy Diagrams

  • Exothermic – more energy is released in new bond formation than in breaking bond in the reactants (energy is released)
  • Endothermic – more energy is absorbed in new bond formation than in breaking bond in the reactants (energy is absorbed)
  • Transition state – a process of change in which bonds are being broken and formed in a reaction
  • Energy of activation – energy difference between reactants and a transition state

Reaction Intermediates

  • Organic reaction occurs, some covalent bonds break and new bonds form and in this multistep reaction mechanisms, as short-lived species call reaction intermediates form.
  • 3 major types: carbocations (are positive), free radicals (one additional electron and are neutral) and carbanions (carbons have formal ownership of five outer-shell electrons and are negative).
  • Particle is charged (carbocations and carbanions).
  • Particle does not have an octet of electrons in the outer shell (carbocations and free radical).
  • Homolytic cleavage – bond cleavage in which the bonding electrons are evenly divided between the two parting atoms (free radical).
  • Heterolytic cleavage – bond cleavage in which the bonding electrons are unevenly divided between the two parting atoms (carbocation and carbanion).

This end the post. In the next part, Part 2 of Berry Berry Easy notes on the Introduction to Organic Reactions for STPM Chemistry will be on the sites of reactions which include multiple bonds, polar bonds, Lewis acids, Lewis bases and their combination. So do click back to this site soon.

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August 24, 2011

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