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Yes, you must always show the arrows when drawing the organic reactions. The arrows represent the electron flow in proposed mechanisms and must be curved. The arrows should also start from the electron rich region, and go towards the region that is electron deficient.
When drawing organic reactions, it is pertinent to use curved arrows in order to represent the electron movement from an e- rich region to a deficient region. In other words, the arrow represents the movement of electrons from a nucleophile to an electrophile. The nucleophile of a reaction is usually a double bond or a lone pair on a molecule, and when there is two electrons moving we use a full arrow head to represent the pair. However, when there is only one electron moving, we use a half arrow head to represent this. Another thing to note, is that the electrophile of the reaction usually has a positive charge or it has a positive pull due to electronegativity.
If you are asked to write a reaction, you do not need to used curved arrows to show electron movement. For example if asked to give an example of an electrophilic addition reaction, you can simple write H2C=CH2 + HBr --> H2BrC-CH3. If you are asked about the mechanism for this reaction, then you do need to show the individual steps and electron movement with curved arrows.
Michael Cheng 1C wrote:do we need to know nucleophiles and electrophiles for the final? What is the difference between them?
The nucleophile is the molecule/ion that donates electrons and the electrophile is the molecule/ion that accepts the electrons.
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