vixintrex wrote:and uh so I hate to press this issue further but if tetrahydroharmine was subjected to a birch we would totally see the left half of the molecule get totally hydrogenated next and next again right?
I'm possibly bad at chemistry so when I think of 'adding a hydrogen to a molecular structure' I could occasionally imagine it could sever an existing molecular bond, especially between two atoms that are different. I don't necessarily understand what bond strength relies on. Is it atomic weight? I know that pi bonds are like twice as strong in relation to external forces like heat, but when subjected to chemical attac they show their true nature as angular differences from a pure relation. daimonds are very strong. I don't know what that has to do with anything. I guess nittrogen is heavier than carbon, so is a carbon nitrogen bond stronger than a carbon-carbon bond?
Press away, this is cool stuff, and my favorite way to learn, teach, or review chemistry is when it is associated with molecules close to my heart. I also agree, seeing the blue color of the solvated electron metal-ammonia complex is enough reason to be interested in this reaction.
There is quite a lot going on here. And quite a large number of possible products, especially if you are putting harmine and harmaline in there, not just THH.
But lets keep things simple for now and talk about what might happen with THH in there.
You are right, you would expect to see the left half (benzene ring) get hydrogenated. But you would not expect to see it become totally hydrogenated, you would expect a partially hydrogenated product (dihydro), a diene as typically expected from a birch reduction. However, this is going to be largely driven by the reaction conditions, whether Na or Li is used, what alcohol proton source you use, the amine used and any cosolvents, the temperature, etc. The main variable that will affect the regioselectivity and reduction product, is actually how fast the protonation step occurs. If you could get dianion formation, you might expect to see the 2,3 bond reduced to form an indoline. You would also expect further reduction products depending on the regioselectivity of the birch reduction, if the diene ended up conjugated with the pyrrole, further reduction to the tetrahydro- product could result, or the associated decomposition products. But because in THH (1) the indole possesses a 6-methoxy group, this is actually going to serve to direct the regioselectivity so we end up with the dihydro product (2), which is going to be stable enough to resist further reduction under these conditions, so I am pretty certain that in the right conditions, you could see this as your primary product. However, since this product is actually now an enol methyl ether, under Lewis acidic conditions you might it expect to hydrolyze down to the ketone product (2a), but under purely the reduction conditions , you probably would not expect this to happen.
As for your questions about bond strength, we are indeed breaking bonds here, but only the pi-bond double bonds. Practically all of the chemistry happening in the birch reduction is happening through and across pi bonds, it all starts when an electron is added into the LUMO of the molecule's pi-system. You aren't going to have C-N cleavage here, although under sufficiently harsh conditions, hydrogenolysis is possible, but not without some kind of catalyst, the beauty of the birch reduction is that it is partial, so it can be employed when you don't want a complete hydrogenation. So the birch is not what you want to use for making cycloalkanes, (it makes cyclohexadienes) for that you would be better off with catalytic hydrogenation, using Pd or Pt metal catalysts. Infact you could see a birch reduction, to get a cyclohexadiene, to break the aromaticity, and then a catalytic hydrogenation, to reduce it down to the alkane. The problem with reductions breaking aromaticity, especially in something like harmaline, or harmine, is that these molecules will re-aromatize if they get the chance, through hydride shifts, or even allowing something like a transfer hydrogenation if there is a catalyst involved.
Your understanding here in your last paragraph is flawed, but you are on the right track at least thinking about it. What makes a bond and what makes it strong and what makes it possible to break. I recommend looking up a first year organic chemistry lecture, focus on things like electronegativity, periodic trends, and molecular orbital theory and hybrid orbital theory. This is what its all about. pi-bonds aren't twice as strong, they are weaker, that is part of why this chemistry is happening, DOUBLE bonds are what you are thinking of (sigma + pi bonds together), double bonds are not twice as strong (because pi bond is not equal to sigma bond) but are almost twice as strong, that must be your confusion. pi-bonds are naturally weaker because their overlap isn't as good. Pi bonds need to rely on parallel orbitals overlapping from two close together atoms, where sigma bonds can have direct overlap. It is not weight, but bond length, that the strength is proportional to, and this makes sense when you think about overlap. Orbital overlap, and electronegativity, are the key components of bond strength. It is very much geometric when it comes to molecules and bonding, but you need to understand the behavior of electrons (fermi mechanics) to see what drives bond formation and bond breaking.
Mindlusion attached the following image(s):

THH birch reduction.jpg
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