[Rutherford]

I was asked to write the formula of the Grinard's reagent and other reactant that make 1-phenyl-ethanol. On the top of the attached image was my first guess, on the bottom is the correct answer, now I am asking why is the bottom one correct?

[Dan]

Consider the basicity of Grignard reagents

[Schrödinger]

I don't get it. Why is the 1st one incorrect? I mean, don't both of them seem plausible? Maybe preparing one is more difficult than the other, but as far as reaction plausibility is concerned, aren't both pathways equally viable?

[Rutherford]

What basicity? It can't release neither H⁺ nor OH^-.
In the answer, there was only the second pathway.

[discodermolide]

What basicity? It can't release neither H⁺ nor OH^-.
In the answer, there was only the second pathway.

I  think Dan means in terms of deprotonation. Basicity is not limited to H⁺ and OH^-
The CH₃-MgX is basic enough to deprotonate the CH₃- and polymerise.

[Dan]

Yeah, point is if you use an enolisable aldehyde you will get the aldol reaction competing.

[Schrödinger]

Wait a second. Isn't the 2nd one the enlolizable aldehyde? So it would make sense if the second combination were to be avoided. But the OP says that's not the case. I thought about aldol too. That reason should favour figure 1. But the answer doesnt seem to agree... That's why I thought aldol is probably not the way to go.

[Rutherford]

Yes, in the bottom one, the proton could be easier transfered to the O atom. In benzaldehyde there is no H atom attached to the α C atom.

[Dan]

Wait a second. Isn't the 2nd one the enlolizable aldehyde? So it would make sense if the second combination were to be avoided. But the OP says that's not the case. I thought about aldol too. That reason should favour figure 1. But the answer doesnt seem to agree... That's why I thought aldol is probably not the way to go.

Sorry, I misread the original post. I think the combination of MeMgBr and PhCHO is the better choice of the two for the reason given above (aldol). So, to clarify, I think Raderfords answer is better than the "correct" answer.

[Rutherford]

Okay, thanks for clearing this up.

[Schrödinger]

One more small doubt regarding this topic : Is there a huge difference in stability between alkyl and aryl magnesium halides? In other words, if you have the option to produce both for 2 different pathways (as above), which pathway is preferred in the lab? (You guys probably would know this from direct experience?)

[Dan]

Both methylmagnesium bromide and phenylmagnesium bromide are common, commercially available laboratory reagents with a decent shelf life if looked after properly. In this case it's is not an issue.

Considering reagent availability is a good general point though.

[orgopete]

I don't get it. Why is the 1st one incorrect? I mean, don't both of them seem plausible? Maybe preparing one is more difficult than the other, but as far as reaction plausibility is concerned, aren't both pathways equally viable?

That was my opinion also. It seems as though something is missing from this question for one of them to be the "correct" answer.