How is Free rad substitution different from halogenation of arenes? How do i tell?
Also,do the state matter? like in alcohol,liquid...
Originally posted by vade:How is Free rad substitution different from halogenation of arenes? How do i tell?
Also,do the state matter? like in alcohol,liquid...
The mechanisms are totally different. You can tell in two ways : the different mechanisms themselves (if you wanna really understand Chemistry, you gotta be prepared to go beyond what JCs teach you, particularly in the area of mechanisms in which JCs only teach the basic syllabus requirements, which does not allow the student to understand Chemistry more deeply), as well as the different reactants/products. For instance, whenever benzene is directly involved, then the benzene is the (guy) nucleophile, while the substituent is the (girl) electrophile.
When the exam qn asks "what kind of reaction is this?" you must specify "halogenation via free radical substitution" (ie. using X2 and UV light, there will be initiation, propagation and termination steps) or "halogenation via electrophilic aromatic substitution" (ie. using X2 with anhydrous Lewis acid catalyst if benzene ring is not activated, or if benzene ring is activated by electron donating by resonance groups such as in phenylamine or phenol, then using X2 in CCl4 for monohalogenation or X2 (aq) for trihalogenation*) or "halogenation via nucleophilic substitution" (eg. using PCl5, SOCl2, etc, I teach my BedokFunland JC students how to draw the mechanisms of using SOCl2 and PCl5 to convert alcohols and carboxylic acids to alkyl halides and acyl halides respectively, to give them a deeper understanding and appreciation of organic chemistry).
* Cambridge can ask you to explain why and how the different solvents results in different extents of electrophilic aromatic substitution. The answer is "the strongly polar protic water solvent induces a stronger temporary dipole in the non-polar X2 molecule, hence X2 (aq) is significantly more electrophilic compared to X2 (in CCl4)."
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1) more extensive consultation with your school teachers, and be willing to ask more qns during tutorial classes.
2) self-learn more using online 'A' level Chemistry websites. Links to such websites can be found on my website : http://infinity.usanethosting.com/Tuition/#H2_Planning_and_other_goodies
3) consider tuition if your family finances allow it; group/class tuition is always cheaper than solo individual tuition. But there are all types of different tutors with different teaching styles, and all types of different students with different learning styles. You may need to try out a few before you find one best suited for yourself.