Working in the field of computational chemistry, it is not unusual, that one focusses on many different topics. The field itself is as broad as chemistry itself as it may be applied to any experimentally raised question. It may be considered as one of the most advanced tools up to date in chemistry.
Its applications may range from simple things as the elucidation of the molecular structure, developing accurate bonding models, or deriving physical and chemical properties. It may also be used to derive complicated reaction mechanisms, characteristic reactions of compounds, classification of novel compound classes and prediction of yet unobserved molecules. Taking this as a basis it may be used in the development of more effective catalysts, it is used in drug design, deriving kinetics and many more.
All of the above is connected via electronic structure theory or more general the approximate solution of Schrödinger's equation. The field of computational chemistry focusses on applying approximations derived by theoretical and/or quantum chemistry to real life questions.
Working in many of these fields is neither uncommon nor unwelcome. Sometimes one particular subject of the starting hypotheses evolves into a huge complex, that may be carried on for years to come, while some other projects are helping in a shorter timescale. Both of them are equally important.
The problem is, each paper I've published is its own research focus without any connection to the next outside of the fact that computational chemistry was used for each.
In this you state, that you already published papers about your subjects. I am guessing these publications were peer reviewed, so they are already proven to be valuable to the scientific community.
Applying quantum chemical calculations to various problems proves, that you are fit in the field. You know how to tackle different questions, you are versatile and your knowledge about the field you are working in is as broad as necessary. It may also show that you are not narrow minded and thinking out-of-the-box.
If the content of your thesis is already published in peer reviewed journals, you will have quite a good chance, that your thesis will remain unread by your peers. Scientific articles tend to be of much higher importance, than the actual thesis.
If your career options include doing a postdoc, than you will still have enough time to specialise yourself. If you want to become a professor yourself you should use that time to develop a specialised, yet versatile and broad research field.
If you plan on working in the chemical industry, the employers are probably more interested in you as a person, your ability to adjust to certain problems, and working according to their standards. Having a broad thesis should not be a hindrance in that case.
However, the title you are currently using may not be very well chosen, since "Relevant Chemical Problems" is a very fuzzy term. On the contrary to some other opinions offered in this thread, I would be very scared of using a long title. Make it as short as possible, while keeping it as precise as necessary.
In conclusion, I do not expect that the title of your thesis will harm your career in any way once you have published in peer reviewed journals.
I know LordStryker from chem.se and therefore I know at least one publication he suggested I read, upon a request of mine. (I will not disclose this source here, because this is up to him.) I am certainly no expert in this particular field of computational chemistry and my understanding might be incomplete. However, I do see the significance of this particular work not only to our community but also to tangenting fields.
I found two other publications, one appeared in a top level journal of our field, the other I cannot judge. From what I understood the presented work is thoroughly, concise and well prepared. I could also see that connecting all these samples is very difficult from a concise topical point of view. However, these all are applications of quantum chemistry, so they all emerged from the same field.
Not receiving a degree for this work is absolutely out of the question.
On a personal note, I would like to state, that it was my own personal decision to get involved in this "discussion" - I was never approached by LordStryker, nor do I have any affiliations with him. Our communication is solely through the se network.