Organic Matter - Organic Chemistry

Organic Chemistry

Measurements of organic matter generally measure only organic compounds or carbon, and so are only an approximation of the level of once-living or decomposed matter. Some definitions of organic matter likewise only consider "organic matter" to refer to only the carbon content, or organic compounds, and do not consider the origins or decomposition of the matter. In this sense, not all organic compounds are created by living organisms, and living organisms do not only leave behind organic material. A clam's shell, for example, while biotic, does not contain much organic carbon, so may not be considered organic matter in this sense. Conversely, urea is one of many organic compounds that can be synthesized without any biological activity.

Very little is currently known about natural organic material. Scientists are unable to crystallize it. This is important because once you can crystallize the material, it can be isolated and studied with x-ray crystallography. This method is standard for determining unknown compounds. Organic matter has not been characterized either and no unique structure is known. The best way to characterize organic matter is by discovering chemical, physical, and thermodynamic properties of the matter. Analytical techniques are currently being discovered to allow this to happen. The only information scientists have is that organic matter is heterogeneous and very complex. Generally, organic matter, in terms of weight, is:

• 45-55% carbon
• 35-45% oxygen
• 3-5% hydrogen
• 1-4% nitrogen

The molecular weights of these compounds can vary drastically, depending on if they repolymerize or not, from 200-20,000 amu. It is also important to know that 10-35% of the carbon present forms aromatic rings. These rings are very stable due to resonance stabilization, so they are difficult to break down. The aromatic rings are also susceptible to electrophilic and nucleophilic attack from other electron-donating or electron-accepting material, which explains the possible polymerization to create larger molecules of organic matter.

There are also reactions that occur with organic matter and other material in the soil to create compounds never seen before. Unfortunately, it is very difficult to characterize these because so little is known about natural organic matter in the first place. Research is currently being done to figure out more about these new compounds and how many of them are being formed.