For those who have Topscore, I have Ochem questions...

[FatalExtraction]

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Can someone just explain to me how do you know where something is going to add to a benzene with a methyl group or NH2 or anything like that...i get the whole ortho meta para directors...but in topscore, i cant tell when the reagent is going to react with the activating groups or attach to the benzene in an ortho/meta/para direction?

For example, you have a benzene with a methyl group attached (i believe its called toluene) and you react it with Br2, hv ----> what would you get?

I dont think i have really even seen these types of questions in kaplan...but i do understand the whole activating groups and deactivating groups...also it would be an anti-mark. addition...so i thought that it would add on the ortho and para directions...however, the Br just added on the CH3...

If any of you have topscore, the questions that I'm referring to are in Test 1, numbers 91 and

also, i was wondering why #97 on test 1 was answer E? thats butadiene has conjugated double bonds right? if you add HCl across a double bond isn't the most stable product the most substituted Cl? how would that double bond get in the center and have the Cl attach at the primary carbon?

sorry if it's a little confusing...it's hard when all of the questions are picture based...thank you for your time and help!

 

[RockstarDMD]

Can someone just explain to me how do you know where something is going to add to a benzene with a methyl group or NH2 or anything like that...i get the whole ortho meta para directors...but in topscore, i cant tell when the reagent is going to react with the activating groups or attach to the benzene in an ortho/meta/para direction?

For example, you have a benzene with a methyl group attached (i believe its called toluene) and you react it with Br2, hv ----> what would you get?

I dont think i have really even seen these types of questions in kaplan...but i do understand the whole activating groups and deactivating groups...also it would be an anti-mark. addition...so i thought that it would add on the ortho and para directions...however, the Br just added on the CH3...

If any of you have topscore, the questions that I'm referring to are in Test 1, numbers 91 and

also, i was wondering why #97 on test 1 was answer E? thats butadiene has conjugated double bonds right? if you add HCl across a double bond isn't the most stable product the most substituted Cl? how would that double bond get in the center and have the Cl attach at the primary carbon?

sorry if it's a little confusing...it's hard when all of the questions are picture based...thank you for your time and help!

In terms of your first question without going into a long explanation just know what reagents can be used with aromatic compounds. For example if you have Toluene like you stated and you react it with something like Br2/Febr3 you will get a Br group at the ortho and para positions with para being the major product.

For your second question do a search on 1,2 and 1,4 additions of conjugated dienes. Learn the rules and this question will look like 1+2=3 to you.

Good Luck

 

[asckwan]

For example, you have a benzene with a methyl group attached (i believe its called toluene) and you react it with Br2, hv ----> what would you get?

I dont think i have really even seen these types of questions in kaplan...but i do understand the whole activating groups and deactivating groups...also it would be an anti-mark. addition...so i thought that it would add on the ortho and para directions...however, the Br just added on the CH3...

If you have Br2 and hv (light) it's a free radical addition. Only when you have Br2 and FeBr3 will you get the O/P addition.

If any of you have topscore, the questions that I'm referring to are in Test 1, numbers 91 and also, i was wondering why #97 on test 1 was answer E? thats butadiene has conjugated double bonds right? if you add HCl across a double bond isn't the most stable product the most substituted Cl? how would that double bond get in the center and have the Cl attach at the primary carbon?

If you have 1,3 butadiene the H will add first to one of the outside carbons, so let's say it adds to Carbon #1. Therefore making the carbocation on the 2nd C. You can then take the extra pair of electrons from the 3 to 4 double bond, move them to be between 2 and 3 so that they carbocation will be on the 4th C and then the Cl will add there, ending up with a H on one end, Cl on the other and a double bond in between.

My teacher told us to think about it in computer terms, 1's and 0's. If H added to Carbon #1 then 2 will be "on", 3 will be "off", 4 will be "on". So Cl can add to any carbon that is "on".

Oh, and one REALLY IMPORTANT RULE!! These additions only happen with all of the double bonds are conjugated!!! If there is a break in conjugation, you cannot continue counting "on"s and "off"s.

I hope this helps you, if not, let me know and I can try again.

 

[FatalExtraction]

on and off ey? ill try to remember that thank you...also, about the br2,hv problem...is there a chart or a list of those reagents that actually mess with the attached group rather than adding to benzene ortho/para/meta?? i dont remember seeing a problem like this and my ochem book isn't sayin much about it...thanks for all of your help