Coal is a natural macromolecule but does not qualify as a polymer because it has no regular, repeating structure based on a restricted set of monomers. The alcohol and carboxylic acid shown as reactants are examples of carbon skeletons similar to those introduced in Figures 1. For each carbon skeleton, the addition of the functional group has created a new chiral center by introducing asymmetry at a formerly symmetrical carbon position. Chemical reactions depicting the formation of two familiar polymers, namely Dacron top and nylon bottom.
The dashed bonds indicate that the repeating, polymeric structures extend indefinitely.
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Values of n can exceed 10 4. The monomers used to form Dacron are a benzene dicarboxylic acid and a C 2 dialcohol.
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The product is a polyester. Nylon is formed by polymerizing two C 6 monomers, a dicarboxylic acid and a diamine. The product is a polyamide. Both polymerizations are condensation reactions. A molecule of water is released for each ester or amide link that is formed. The depositional environment i. It attracts attention because of the tendency of organic compounds to react with each other, it often constitutes 99 percent of the organic carbon in a sedimentary rock. Kerogen, a macromolecule so large that it is not soluble in any solvent, is isolated by dissolving everything else.
A sedimentary rock is ground to produce a powder.
Carbon-Rich Compounds - From Molecules to Materials
Small organic molecules are extracted using organic solvent. Inorganic material, the rocky matrix, is dissolved using hydrochloric and hydrofluoric acids. The kerogen remains. Ideas about its molecular structure which will vary depending on the specific algal and microbial precursors and conditions, such as the abundance of H 2 S, in the depositional environment can be obtained by chemical and thermal degradation of the macromolecule.
Insoluble, macromolecular, carbonaceous debris will form wherever reactive organic molecules are stored in close proximity. A terrestrial example of such material is kerogen. An extraterrestrial counterpart is found in carbon-rich meteorites. The exploration of organic cosmochemistry is not a search for life but an examination of all of the processes that have shaped the existence of life on Earth and, perhaps, elsewhere in the universe.
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The keys are to look in the right places, to collect and examine the right molecular mixtures, and to patiently and systematically extend the organic chemical analyses in ways that will maximize the precision with which interpretations can be made. Each organic molecule provides information about its origins through details of its structure. Within the carbon skeleton, the number of rings and multiple bonds which is to say the ratio of hydrogen to carbon, since each ring, double bond, or triple bond decreases the number of bonds to hydrogen provides information about the availability of hydrogen at the site of molecular synthesis.
Structures rich in multiple bonds suggest that reactive hydrogen was rare during assembly of the carbon skeleton. Some carbon skeletons, for example those containing small 3- or 4-membered rings, incorporate quite a bit of strain i.
If such rings have survived, they suggest that the molecule was unable to rearrange as it was formed and that the molecule has been cool since the time of its synthesis. Similarly, biotic processes synthesize many unique chemical structures. The nature of the functional group carries further information. For example, alcohols, aldehydes, and carboxylic acids indicate progressively higher levels of oxidation. The survival of functional groups that would react with water e. Again, the extension and elaboration of interpretations are limited only by the quality of the information about the numbers and types of functional groups.
Within mixtures of molecules, discernible patterns can be interpreted in terms of controlling mechanisms. A preference for molecules with even numbers of carbon atoms, for example, would indicate that C 2 reactive units had been important in the environment of synthesis. A prevalence of two-dimensional, sheet-like structures would suggest formation on surfaces.
In general, the properties of catalysts can be discerned from the extent to which some products have been favored over others. Where catalysis has been controlled precisely, the structural preferences can be absolute. At this, life, i. The common, biologically synthesized amino acids, the monomers used in the synthesis of proteins, provide an illustrative example. By definition, an amino acid contains both an amine group and a carboxylic acid group see Figure 1.
The carbon skeletons of the amino acids used in proteins contain up to 10 carbon atoms and up to six double bonds or rings. With two different functional groups, 10 carbon atoms, and varying numbers of rings and double bonds, the number of possible molecular structures is astronomical. From among those structures, each cell makes only 20 for inclusion in proteins.
Each contains the particular assembly of functional groups identified in Figure 1. As indicated in Figure 1. At that point, the biosynthetic process is even stereoselective, producing only one of the stereoisomers of each amino acid.
Encountering that mixture of materials, with only 20 structures from among the possible millions and only one chiral form of each, anyone would recognize the catalyst as being a biological process. Abiotic processes are less precisely selective, but the logical process of working backward from the analysis of an organic mixture to inferences about the mechanism of synthesis is no different. Molecules also carry information about their origins in one rather unconventional way. The elements that are most important in organic chemistry—carbon, hydrogen, nitrogen, oxygen, and sulfur—all happen to have multiple stable isotopes specifically, 1 H and 2 H; 12 C and 13 C; 14 N and 15 N; 16 O, 17 O, and 18 O; and 32 S, 33 S, 34 S, and 36 S.
Isotope effects associated with industrial processes such as the cracking of petroleum or electrolytic production of H 2 from H 2 O also fractionate the stable. In the cosmos, isotopic abundances vary not only as a result of isotope effects but also because of variations in nucleosynthetic processes. Isotopic evidence can be used in two general ways. First, mixtures of compounds from different sources can be recognized. Compounds in one population of molecules might, for example, all be depleted in 13 C.
Another population might be distinguished by enrichment in 2 H. In favorable cases, two or more populations can be recognized and their isotopic characteristics defined well enough that, when a particular compound happens to have multiple origins, mixing equations can be used to determine the proportion attributable to each source. Second, precursor-product and other genetic relationships can be recognized.
If compound A is consistently depleted in 13 C relative to compound B by a few parts per thousand, it is likely that A derives from B and that the reaction relating A and B has a kinetic isotope effect.
If one family of structurally related compounds has isotopic abundances that are similar or that covary systematically, it is likely that all members of the family share a common source, and if another compound is related structurally but does not conform to the isotopic pattern, it must have a separate origin in spite of the structural relationship.
The chemistry of carbon leads to extraordinary variations in the structures of organic molecules. Factors influencing those variations include the following:.
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The abundances of reactive forms of some of the most abundant elements in the cosmos, namely hydrogen, nitrogen, and oxygen;. The nature of any catalysts—ranging from random solid surfaces to other organic molecules—that were present in the environment of synthesis. Knowledge of organic chemistry is so advanced, and the information content of mixtures of organic compounds i. Given the structures and relative abundances of organic compounds from samples of cosmochemical interest, it may be possible to work backward and to reconstruct the physical and chemical conditions prevailing at the times of their synthesis and throughout their subsequent history.
With regard to the indicators that might differentiate between a biotic and an abiotic origin for particular organic compounds, the task group found that the most compelling indicators of an abiotic origin include the following:. The presence of a smooth distribution of organic compounds in a sample, e.
The presence of all possible structures, patterns, isomers, and stereoisomers in a subset of compounds such as amino acids;. The lack of depletions or enrichments of certain isotopes with respect to the isotopic ratio normally expected. Likewise, the converse of the above items are indicators of possible biotic synthesis.
Thus, the following are indicators of a biotic origin:. The presence of an irregular distribution of organic compounds in a sample, e. The presence of only a small subset of all possible structures, patterns, isomers, and stereoisomers;. The depletion or enrichment of certain isotopes with respect to the isotopic ratio normally expected. However, some abiotic processes can mimic biotic ones and vice versa, and inferences will necessarily be based on several indicators and will, of course, be probabilistic.
Simoneit and J. Rushdi and B. See, for example, B. The sources, distributions, and transformation of organic compounds in the solar system are active study areas as a means to provide information about the evolution of the solar system and the possibilities of life elsewhere in the universe. There are many organic synthesis processes, however, and ambiguity surrounds the relative effectiveness of these processes in explaining the distribution of organic compounds in the solar system.
As a consequence, NASA directed the NRC to determine what processes account for the reduced carbon compounds found throughout the solar system and to examine how planetary exploration can advance understanding of this central issue. This report presents a discussion of the chemistry of carbon; an analysis of the formation, modification, and preservation of organic compounds in the solar system; and an assessment of research opportunities and strategies for enhancing our understanding of organic material in the solar system.
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Carbon-Rich Compounds: From Molecules to Materials
I —The Chemistry of Carbon. Page 10 Share Cite. This page intentionally left blank. Page 11 Share Cite. Page 12 Share Cite. What other chemical elements and compounds were present? What was the pressure? What mineral surfaces were available? What sort of electromagnetic radiation was present? Page 13 Share Cite. Aliphatic Homologs. Page 14 Share Cite. Other Carbon Compounds.
The following structures will require you to download a molecular modeling viewer to view the pdb files. We highly reccommend you take a look at " Viewing Molecules at Home and School " and download a software package. Questions or Comments? MathMol Home Page. Introductory Comments. What is Molecular Modeling? Why is Molecular Modeling Important? What do some common molecules look like? Where's the Math? Carbon 3 Ways. Carbon Compounds. Water and Ice. Water and Ice pt. How to view structures in class or at home.
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