Organic Chemistry for Health Sciences Lecture 5 PDF

Organic chemistry for health sciences By Dr/ Rasha Shoaib Lecturer of Biochemistry The Functional Group *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...

Organic chemistry for health sciences By Dr/ Rasha Shoaib Lecturer of Biochemistry The Functional Group *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. *Organic molecules vary greatly in size and when focusing on functional groups, we want to direct our attention to the atoms involved in the functional group. *As a result, the abbreviation R is used in some examples. The letter R is used in molecular structures to represent the “Rest of the molecule”. *R group consists of a group of carbon and hydrogen atoms of any size. It is used as an abbreviation since a group of carbon and hydrogen atoms does not affect the functionality of the compound. In some molecules, you will see R, R’, or R’’ which indicates that the R groups in the molecule can be different from one another. For example, R might be –CH2CH3 while R’ is –CH2CH2CH2CH3. Alcohols An alcohol is an organic compound with a hydroxyl (OH) functional group on an aliphatic carbon atom. *Because OH is the functional group of all alcohols, we often represent alcohols by the general formula ROH, where R is an alkyl group. *Alcohols are common in nature. *Most people are familiar with ethyl alcohol (ethanol), the active ingredient in alcoholic beverages, but this compound is only one of a family of organic compounds known as alcohols. The family also includes such familiar substances as cholesterol and the carbohydrates. *Methanol (CH3OH) and ethanol (CH3CH2OH) are the first two members of the homologous series of alcohols. Nomenclature of alcohols Alcohols with one to four carbon atoms are frequently called by common names, in which the name of the alkyl group is followed by the word alcohol: *According to IUPAC, the name of alcohol comes from the hydrocarbon from which it was derived. *The final -e in the name of the hydrocarbon is replaced by -ol, and the carbon atom to which the –OH group is bonded is indicated by a number placed before the name. 2-pentanol  Name the following molecule: 2-methyl-2-pentanol *The IUPAC adopted new nomenclature guidelines in 2013 that require this number to be placed as an “infix” rather than a prefix. *For example, the new name for 2-propanol would be propan-2-ol. Name the following molecule according to the guidelines adopted in 2013? butan-2-ol "Always place the OH on the lowest possible number for the chain." In the previous example, if the carbon atoms were numbered from left to right then the OH would have been placed on the third carbon and the molecule would have been named butan-3-ol, but butan-2-ol is the more preferred name. Name the following molecules according to the guidelines adopted in 2013? propan-2-ol hexan-2-ol *Some of the common names reflect a compound’s classification as secondary (sec-) or tertiary (tert-). These designations are not used in the IUPAC nomenclature system for alcohols.  Methanol (Methyl Alcohol) *Methanol, also known as methyl alcohol among others, is a chemical with the formula CH3OH (a methyl group linked to a hydroxyl group, often abbreviated MeOH). Methanol acquired the name wood alcohol because it was once produced chiefly by the destructive distillation of wood. *Today, methanol is mainly produced industrially by hydrogenation of carbon monoxide. CO(g) + 2H2(g) → CH3OH(l) *Methanol is the simplest alcohol, consisting of a methyl group linked to a hydroxyl group. *It is a light, volatile, colorless, flammable liquid with a distinctive odor similar to that of ethanol (drinking alcohol). *At room temperature, it is a polar liquid. *With more than 20 million tons produced annually, it is used as a fuel additive and as a precursor to other commodity chemicals, including formaldehyde, acetic acid, methyl tert-butyl ether, as well as a host of more specialized chemicals. *Methanol may cause birth defects of the central nervous system in humans. *Chronic poisoning from repeated exposure to methanol vapor may produce: 1) Inflammation of the eye (conjunctivitis). 2) Recurrent headaches. 3) Giddiness. 4) Insomnia. 5) Stomach disturbances. 6) Visual failure.  Ethanol (Ethyl Alcohol) *Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is a chemical compound, a simple alcohol with the chemical formula C2H6O. *Its formula can be also written as CH3−CH2−OH or C2H5OH (an ethyl group linked to a hydroxyl group), and is often abbreviated as EtOH. *Ethanol is a volatile, flammable, colorless liquid with a slight characteristic odor. *It is a psychoactive substance and is the principal type of alcohol found in alcoholic drinks. Ethanol is naturally produced by the fermentation of sugars by yeasts or via petrochemical processes, and is most commonly consumed as a popular recreational drug. *Ethanol is the alcohol produced by some species of yeast that is found in wine, beer, and distilled drinks. *It has long been prepared by humans harnessing the metabolic efforts of yeasts in fermenting various sugars: Large quantities of ethanol (for industrial use) are synthesized from the addition reaction of water with ethylene using an acid as a catalyst: *Ethanol also has medical applications as an antiseptic and disinfectant. *The compound is widely used as a chemical solvent, either for scientific chemical testing or in the synthesis of other organic compounds. It is a vital substance used across many different kinds of manufacturing industries. *Ethanol is also used as a clean-burning fuel source. Multifunctional Alcohols *A polyol is an organic compound containing multiple hydroxyl groups. Examples of polyols include ethylene glycol, propylene glycol, and glycerol. *Alcohols containing two or more hydroxyl groups can be made. 1) Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound with the formula (CH2OH)2. *It is mainly used for two purposes: 1) As a raw material in the manufacture of polyester fibers. 2) For antifreeze formulations. *It is an odorless, colorless, sweet-tasting, viscous liquid. Ethylene glycol is toxic. Household pets are especially susceptible to ethylene glycol poisoning from vehicle antifreeze leaks. 2) Propylene glycol (IUPAC name: propane-1,2-diol) is an organic compound with the chemical formula CH3CH(OH)CH2OH. *It is a viscous, colorless liquid that is nearly odorless but possesses a faintly sweet taste. *Containing two alcohol groups, it is classed as a diol. *It is miscible with a broad range of solvents, including water, acetone, and chloroform. *In general, glycols are non-irritating, and have very low volatility and very low toxicity. 1) 45% of propylene glycol produced is used as chemical feedstock for the production of unsaturated polyester resins. 2) Propylene glycol is also used in various edible items such as coffee-based drinks, liquid sweeteners, ice cream, whipped dairy products, and soda. 3) Vaporizers used for the delivery of pharmaceuticals or personal-care products often include propylene glycol among the ingredients. 4) In alcohol-based hand sanitizers, it is used as a humectant to prevent the skin from drying. 5) Propylene glycol is used as a solvent in many pharmaceuticals, including oral, injectable, and topical formulations, such as for diazepam and lorazepam which are insoluble in water. 6) Certain formulations of artificial tears, such as Systane, use proplyene glycol as an ingredient. 7) Propylene glycol is frequently used as a substitute for ethylene glycol in low toxicity, environmentally friendly automotive antifreeze. 8) It is also used to winterize the plumbing systems in vacant structures. 3) Glycerol (IUPAC name: 1,2,3-propanetriol) also called glycerine or glycerin is a simple polyol compound. *It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. *The glycerol backbone is found in many lipids which are known as glycerides. *It is widely used in the food industry as a sweetener and humectant in pharmaceutical formulations. *Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. 1) In food and beverages, glycerol serves as a humectant, solvent, and sweetener, and may help preserve foods. 2) It is also used as filler in commercially prepared low-fat foods (e.g., cookies), and as a thickening agent in liqueurs. 3) Glycerol and water are used to preserve certain types of plant leaves. 4) As a sugar substitute, it has approximately 27 kilocalories per teaspoon (sugar has 20) and is 60% as sweet as sucrose. 5) It does not feed the bacteria that form plaques and cause dental cavities. 6) As a food additive, glycerol is labeled as E number E422. It is added to icing (frosting) to prevent it from setting too hard. 7) Glycerol is used in medical, pharmaceutical, and personal care preparations, often as a means of improving smoothness, providing lubrication, and as a humectant. 8) Ichthyosis and xerosis have been relieved by the topical use glycerin. 9) It is found in allergen immunotherapies, cough syrups, elixirs and expectorants, toothpaste, mouthwashes, skin care products, shaving cream, hair care products, soaps, and water-based personal lubricants. 10) In solid dosage forms like tablets, glycerol is used as a tablet-holding agent.