[Plumbum]

hi

can anyone tell me if this mechanism, which is supposed to be a nucleophilic substitution is correct?

thank u

[pgk]

Absolutely not.
H2SO4 behavior is wrongly represented.
NaBr bond is ionic and not homopolar.

[Plumbum]

Why? H2So4 is used to protonate the OH-Group, because OH ist not a good leaving group.

[Plumbum]

..and NaBr is supposed to be the nucleophile. I drew the arrow wrong though, its supposed to attack the C and H2O acts as the leaving group

[pgk]

The electron transfer arrow is in the inverse way, for H2SO4 and the nucleophile is the bromide anion (Br-) and not the NaBr (the ionization of NaBr is quantitative}.

[Plumbum]

Ok so I need to chang the direction of the arrow for the protonation with the h2so4.
And should write Na+ br- instread of nabr then? and let the br- attack?

[pgk]

Yes.

[Dan]

Also: You have drawn bromide attacking O, this is incorrect.

[Plumbum]

so it should be correct like this. right?

[pgk]

Much better. The arrow from butanol to H2SO4 is in the right direction. But something is still missed. The leaving (nuclophyge) arrow on sulfuric acid is not represented.
Try to draw the arrows correctly at the first step. The attacking arrow starts from the electron pair of the butanol oxygen to the hydrogen of the one hydroxyl group of sulfuric acid and the leaving arrow starts from the H-O bond of that hydroxyl group and forms the bisulfate anion:
CH3CH2CH2CH2-O(¨)H  +  H-OSO3H  →  CH3CH2CH2CH2-OH2(+)   +    (-)OSO3H
The above symbols in parenthesis, reperesent the electron pair and the positive and negative charge, respectively.