If someone walks up to you and demands "How do you know what molecules look like?" or "Why do molecules behave as they do?" you can now provide answers invoking scanning probe microscopy, x-ray diffraction (including density difference maps), and quantum mechanics (including HOMO/LUMO theory). Of course your level of confidence will increase as you master more of the lore of organic chemistry.
The possibility of providing such straightforward, convincing answers is quite recent:
X-rays were discovered just over a century ago (1895) and have been applied to determine the structure of complex organic molecules only since I was in grade school, which doesn't seem so long ago to me. When I was in graduate school one could get a Ph.D. by determining the structure of one molecule of modest size. Now you have to determine the structure of the ribosome to get the world's attention.
Schrödinger devised his Equation just over 3/4 of a century ago (1926). Its application to organic molecules has become widespread only since the 1960s, when I was in graduate school. It has become routine for general chemists only with the availability of programs like MacSpartan, and computers to run them on, within the last decade.
Scanning probe microscopy is not a whole lot older than you are (born in 1981).
Here is a really amazing fact :
When these powerful techniques came along and revealed the intimate structure of matter, no one was surprised! Chemists already knew what molecules looked like and how they behaved!
There are two reasons that we should study how it was that chemists already knew so much about molecules.
First, because invention of the organic molecular model is a milestone in the history of the human mind. Every educated person should know it, and be proud of it, and be able to use its evolution as a model for evaluating current scientific developments and setting them in perspective. It shows how science works at its best.
Second, because the empirical molecular model that our predecessors developed, together with its accompanying notation and nomenclature, remains the single most powerful tool for the everyday practice of chemistry. If we don't know how it developed, we will neither be able to manipulate it properly nor be aware of its strengths and limitations.
In retrospect we will see that the way in which the empirical molecular theory of organic chemistry evolved over 150 years was amazingly logical - from one big C to the next:
This historical progression was so logical that it makes sense to learn the subject chronologically.
Each stage of development included:
Experimental results that required new theory,
Nomenclature/Notation that embody the theory, and
Real human people who knitted everything together, but not without dropping their share of stitches. There is a temptation to consider these pioneers as mythic heros, but in many ways they resemble current scientists. Understanding how they succeeded and failed remains instructive for modern scientists.
We will touch all of these aspects, but if any one of them is to be given primacy for chemistry, my vote goes to experimental results. Knowing the facts, and the sequence in which they were discovered, one could slowly reconstruct the theory. Without facts there is only nonsense like Occult Chemistry.
Perhaps the greatest contribution of our predecessors was in filtering - knowing or guessing which existing facts were worth focussing attention on and which new facts would be worth collecting. In science, as in other aspects of life, you can go a long way on good taste and good luck.
The point of our studying organic chemical history is not to memorize the names, dates, and birthplaces of heros and villains. It is to understand the facts and logic on which this discipline is based. Knowing some key dates helps keep the logic straight. For most students personalities help make it memorable.