# 8: Organic Chemistry


Photosynthesis involves a whole series of reactions with many chemicals, enzymes, breaking and making chemical bonds, the transfer of electrons and H+ ions, and other chemical processes. The elucidation of the actual steps of photosynthesis-a process still unduplicated artificially-is a major achievement of modern chemistry.

All life on Earth is ultimately based on photosynthesis. Photosynthesis is the process by which plants absorb CO2 and H2O from their environment and, in the presence of sunlight, convert those substances into a simple sugar (glucose) and ultimately starches and other building blocks of life. The net photosynthesis chemical reaction is as follows:

$6CO_{2}+6H_{2}O \overset{light}{\rightarrow} C_{6}H_{12}O_{6}+6O_{2}\nonumber$

Oxygen is also a product of photosynthesis. Most forms of animal life (including people) depend on oxygen to breathe, which makes plants indispensable. Virtually all food sources come from plants, eaten either directly (as fruits, vegetables, or grains) or indirectly (as feedstock for meat animals such as cattle, poultry, pigs, sheep, goats, and the like). Plants are absolutely necessary for life to exist.

The net reaction for photosynthesis is misleadingly simple. A series of reactions, called light-dependent reactions, start by the absorption of light by pigments (not just chlorophyll, as commonly misunderstood) in plant cells. This is followed by a series of light-independent reactions, so named not because they happen in the dark, but because they do not directly involve light. However, light-independent reactions involve the products of reactions stimulated by light, so they ultimately depend on light. The whole series of reactions involves many chemicals, enzymes, breaking and making chemical bonds, the transfer of electrons and H+ ions, and other chemical processes. The elucidation of the actual steps of photosynthesis—a process still unduplicated artificially—is a major achievement of modern chemistry.

• 8.1: Organic Chemistry
Today organic chemistry is the study of the chemistry of the carbon compounds, and inorganic chemistry is the study of the chemistry of all other elements. Organic chemistry is the study of carbon compounds, nearly all of which also contain hydrogen atoms.
• 8.2: Structures and Names of Alkanes
Simple alkanes exist as a homologous series, in which adjacent members differ by a $$CH_2$$ unit.
• 8.3: Branched-Chain Alkanes
Alkanes with four or more carbon atoms can exist in isomeric forms.
• 8.4: Condensed Structural and Line-Angle Formulas
Condensed chemical formulas show the hydrogen atoms (or other atoms or groups) right next to the carbon atoms to which they are attached. Line-angle formulas imply a carbon atom at the corners and ends of lines. Each carbon atom is understood to be attached to enough hydrogen atoms to give each carbon atom four bonds.
• 8.5: Prelude to Unsaturated and Aromatic Hydrocarbons
The two simplest unsaturated compounds—ethylene (ethene) and acetylene (ethyne)—were once used as anesthetics and were introduced to the medical field in 1924. However, it was discovered that acetylene forms explosive mixtures with air, so its medical use was abandoned in 1925. Ethylene was thought to be safer, but it too was implicated in numerous lethal fires and explosions during anesthesia. Even so, it remained an important anesthetic into the 1960s, when it was replaced by nonflammable anes
• 8.6: Functional Groups
With over twenty million known organic compounds in existence, it would be very challenging to memorize chemical reactions for each one. Fortunately, molecules with similar functional groups tend to undergo similar reactions. A functional group is defined as an atom or group of atoms within a molecule that has similar chemical properties whenever it appears in various compounds. Even if other parts of the molecule are quite different, certain functional groups tend to react in certain ways.
• 8.7: Narcotics
Narcotic agents are potent analgesics which are effective for the relief of severe pain. Analgesics are selective central nervous system depressants used to relieve pain. The term analgesic means "without pain". Even in therapeutic doses, narcotic analgesics can cause respiratory depression, nausea, and drowsiness. Long term administration produces tolerance, psychic, and physical dependence called addiction.

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