problem with organic chem

[OU11BB]

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I cant seem to get this into my head, maybe someone here can help. syn and anti addition. 95% of the time i can follow all steps of the addition except the main one is it syn or anti orientation. I must be looking over a rule everytime. can someone please explain what i should be looking for. I think steric hindrance is a concept to understand. do H's and D's always and syn and halides, OH's, and larger groups add syn?

 

[DATlongshui]

I thought if it is SN2 (strong nucleophile), it is anti, just because the way SN2 works; if the reaction takes place on metal surface, it has to be syn. Then for hydroboration, it is syn and attacks to less sterically hindered carbon.

 

[wantVCUdental]

I cant seem to get this into my head, maybe someone here can help. syn and anti addition. 95% of the time i can follow all steps of the addition except the main one is it syn or anti orientation. I must be looking over a rule everytime. can someone please explain what i should be looking for. I think steric hindrance is a concept to understand. do H's and D's always and syn and halides, OH's, and larger groups add syn?

It depends on your reagents, in cases of H's and D's where you catalyze with any metal (usually with a Pt), when you use metal, those H's are first fixated on to the metal so when they are added to the double bond, there's only 1 orientation they can add to-SYN

In cases where you have the electrons attacking one atom at a time, then you get anti, for example HBr, Br actually forms a bromonium ion across the double bond, so the hydrogen can only attk from below 🙂

 

[OU11BB]

It depends on your reagents, in cases of H's and D's where you catalyze with any metal (usually with a Pt), when you use metal, those H's are first fixated on to the metal so when they are added to the double bond, there's only 1 orientation they can add to-SYN

In cases where you have the electrons attacking one atom at a time, then you get anti, for example HBr, Br actually forms a bromonium ion across the double bond, so the hydrogen can only attk from below 🙂

What about problem 123 in 2008 version of destroyer. start with cyclohexane 1 step is Br2,hv 2nd C2H5O-Na+ in C2H5OH 3rd OsO4, NaHSO3 the OH's add syn there is no explanation in the book. Does it have to do anything with the ring in chair conformation one is axial and one is equatorial?

 

[wantVCUdental]

What about problem 123 in 2008 version of destroyer. start with cyclohexane 1 step is Br2,hv 2nd C2H5O-Na+ in C2H5OH 3rd OsO4, NaHSO3 the OH's add syn there is no explanation in the book. Does it have to do anything with the ring in chair conformation one is axial and one is equatorial?

I don't have that book... so i don't know the question, Br2,hv=radical addition, base C2H5O- is for deprotonation, OsO4 is for adding OH in syn fashion(ALWAYS, whenever you see OsO4, that's always syn addition, just memorize that) across double bond

 

[OU11BB]

Ok thanks VCU. did you get your interview yet?

 

[wantVCUdental]

Ok thanks VCU. did you get your interview yet?

no 🙁, i feel hope is slim now...
hope i hear something good from schools soon