In a lab experiment I added Br2 to hydrocarbons cyclohexane, cyclohexene, and toluene. A loss of color would indicate a reaction took place. Only the cyclohexene lost color and turned clear. I guess this means that the Br2 broke the cyclohexenes double bonds but why didn't bromine react with the other two hydrocarbons?

Br2 adds across the double bond in cyclohexene. Cyclohexane and aromatic hydrocarbons (toluene) don't react in the4 cold and with no uv light.

The loss of color in the presence of bromine (Br2) indicates a reaction between the bromine and the hydrocarbon. In this case, since only cyclohexene lost its color and turned clear, it suggests that a reaction occurred between cyclohexene and bromine.

Cyclohexane and toluene, on the other hand, did not show any color change, which implies that bromine did not react with these hydrocarbons to the same extent as it did with cyclohexene. The reason for this lies in the difference in the chemical structure of these hydrocarbons.

Cyclohexane is a saturated hydrocarbon, meaning it consists entirely of single bonds between carbon atoms and contains no double bonds. Bromine does not readily react with saturated hydrocarbons like cyclohexane because the C-C bonds in saturated hydrocarbons are relatively stable and less reactive. Therefore, bromine cannot break the C-C bonds in cyclohexane, resulting in no color change.

Toluene, on the other hand, contains a benzene ring in its structure and has delocalized pi electrons. These pi electrons contribute to the stability and resistance of aromatic hydrocarbons, like toluene, to undergo reactions with electrophiles such as bromine. While bromine can react with aromatic hydrocarbons under specific reaction conditions or with the presence of a catalyst, without any external influence, bromine does not readily react with toluene, leading to no color change.

In summary, the difference in reactivity towards bromine among cyclohexane, cyclohexene, and toluene stems from the presence of double bonds in cyclohexene, which makes it more susceptible to react with electrophiles like bromine. The absence of double bonds in cyclohexane and the greater stability of aromatic compounds, like toluene, prevent them from undergoing a similar reaction.