The number of stereoisomers obtained by bromination of trans-2-butene is

The bromination of trans-2-butene results in the formation of 2,3-dibromobutane.

Step 1: Bromine adds across the double bond of trans-2-butene in a reaction known as halogen addition.

Step 2: The bromine molecule is polarizable, and the bromine-bromine bond is weak. This allows the bromine molecule to react with the electron-rich double bond of the trans-2-butene.

Step 3: The bromine molecule forms a cyclic bromonium ion with the carbon atoms of the double bond. This is a three-membered ring structure which is highly strained and reactive.

Step 4: A second bromide ion attacks the bromonium ion from the opposite side, leading to the formation of 2,3-dibromobutane.

Step 5: The product, 2,3-dibromobutane, has two chiral centers, which means it can exist as two pairs of enantiomers.

Therefore, the number of stereoisomers obtained by bromination of trans-2-butene is 4. These include two pairs of enantiomers: (R,R)-2,3-dibromobutane and (S,S)-2,3-dibromobutane, and (R,S)-2,3-dibromobutane and (S,R)-2,3-dibromobutane.