organic chemistry - The most common elements in functional group - Chemistry Stack Exchange up vote 4 down vote The most common element present in organic functional groups is carbon, $\ce{C}$, which is also the most common element in organic compounds. All functional groups are defined as some other atoms attached to at least one carbon atom. The second most common element in organic compounds is hydrogen, $\ce{H}$, but $\ce{H}$ is not necessary for the formal definition of many functional groups. The third most common element is oxygen, $\ce{O}$, which is an essential element in the definition of many functional groups, followed by nitrogen, $\ce{N}$, and then sulfur, $\ce{S}$, phosphorous, $\ce{P}$, the halogens, and boron, $B$.

Occurrence frequency in functional group definition: In the lists of functional groups below, the prevalence of certain elements by requirement in the formal definition of that functional group is: $\ce{C} \ 100\%,\ \ce{O}\ 47\%,\ \ce{N}\ 30\%,\ \ce{S}\ 19\%,\ \ce{H}\ 13\%,\ \ce{P}\ 9\%,\ \ce{F,\ Cl,\ Br,\ I, B}\ 4\%$ Hydrocarbons: Alkane and Cycloalkane - all $sp^3$ $\ce{C-C}$ and $\ce{C-H}$ bonds: $\ce{-CH2-CH2 -}$ Alkene - at least two $sp^2$ carbon atoms sharing at least one $\ce{C=C}$ bond: $\ce{-CH=CH -}$ Allene - at least one cumulated diene where the middle carbon is $sp$: $\ce{-CH=C=CH -}$ Alkyne - at least two $sp$ hybridized carbon atoms sharing at least one $\ce{C#C}$ bond: $\ce{-C3C

 -}$ Aromatic ring - a cyclic planar fully conjugated polyene containing $4n+2 \ \pi$ electrons, where $n\geq0$ is an integer.

See benzene . In all of the hydrocarbon functional groups, the hydrogen atoms are not necessary. They can often be replaced by carbon or heteroatoms (not $\ce{C}$ or $\ce{H}$) and you still have the functional group. That being said, hydrogen is the second most common element in organic molecules, even if it is not required for the formal definition of some functional groups. Functional groups with single bonds between carbon and heteroatoms. In most of these functional groups, the $\ce{H}$ atoms shown are part of the definition. The letter $\ce{R}$ represents hydrocarbon groups, although for a few groups, it can represent $H$. The Chemical Basis for Life About Watch and Favorite Watch Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made. Favorite Favoriting this resource allows you to save it in the “My Resources” tab of your account. There, you can easily access this resource later when you’re ready to customize it or assign it to your students. The Chemical Basis for Life Carbon is the most important element to living things because it can form many different kinds of bonds and form essential compounds.

Learning Objective Explain the properties of carbon that allow it to serve as a building block for biomolecules Key Points All living things contain carbon in some form. Carbon is the primary component of macromolecules , including proteins , lipids , nucleic acids, and carbohydrates . Carbon's molecular structure allows it to bond in many different ways and with many different elements . The carbon cycle shows how carbon moves through the living and non-living parts of the environment. Terms Register for FREE to remove ads and unlock more features! Learn more Full Text Carbon is the fourth most abundant element in the universe and is the building block of life on earth. On earth, carbon circulates through the land, ocean, and atmosphere, creating what is known as the Carbon Cycle. This global carbon cycle can be divided further into two separate cycles: the geological carbon cycles takes place over millions of years, whereas the biological or physical carbon cycle takes place from days to thousands of years. In a nonliving environment, carbon can exist as carbon dioxide (CO2), carbonate rocks, coal, petroleum, natural gas, and dead organic matter. Plants and algae convert carbon dioxide to organic matter through the process of photosynthesis , the energy of light.

All living things contain carbon in some form, and carbon is the primary component of macromolecules, including proteins, lipids, nucleic acids, and carbohydrates. Carbon exists in many forms in this leaf, including in the cellulose to form the leaf's structure and in chlorophyll, the pigment which makes the leaf green. Carbon is Important to Life In its metabolism of food and respiration , an animal consumes glucose (C6H12O6), which combines with oxygen (O2) to produce carbon dioxide (CO2), water (H2O), and energy, which is given off as heat. The animal has no need for the carbon dioxide and releases it into the atmosphere. A plant, on the other hand, uses the opposite reaction of an animal through photosynthesis. It intakes carbon dioxide, water, and energy from sunlight to make its own glucose and oxygen gas. The glucose is used for chemical energy , which the plant metabolizes in a similar way to an animal. The plant then emits the remaining oxygen into the environment. Cells are made of many complex molecules called macromolecules, which include proteins, nucleic acids (RNA and DNA), carbohydrates, and lipids.

The macromolecules are a subset of organic molecules (any carbon-containing liquid, solid, or gas) that are especially important for life. The fundamental component for all of these macromolecules is carbon. The carbon atom has unique properties that allow it to form covalent bonds to as many as four different atoms, making this versatile element ideal to serve as the basic structural component, or "backbone," of the macromolecules. Structure of Carbon Individual carbon atoms have an incomplete outermost electron shell . With an atomic number of 6 (six electrons and six protons), the first two electrons fill the inner shell, leaving four in the second shell. Therefore, carbon atoms can form up to four covalent bonds with other atoms to satisfy the octet rule . The methane molecule provides an example: it has the chemical formula CH4. Each of its four hydrogen atoms forms a single covalent bond with the carbon atom by sharing a pair of electrons. This results in a filled outermost shell. Organic Chemistry - American Chemical Society Organic Chemistry What Is Organic Chemistry?

Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds, which include not only hydrocarbons but also compounds with any number of other elements, including hydrogen (most compounds contain at least one carbon–hydrogen bond), nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur. This branch of chemistry was originally limited to compounds produced by living organisms but has been broadened to include human-made substances such as plastics. The range of application of organic compounds is enormous and also includes, but is not limited to, pharmaceuticals, petrochemicals, food, explosives, paints, and cosmetics. Where Is Organic Chemistry Used? Organic chemistry is a highly creative science in which chemists create new molecules and explore the properties of existing compounds. It is the most popular field of study for ACS chemists and Ph.D. chemists. Organic compounds are all around us. They are central to the economic growth of the United States in the rubber, plastics, fuel, pharmaceutical, cosmetics, detergent, coatings, dyestuff, and agrichemical industries, to name a few. The very foundations of biochemistry, biotechnology, and medicine are built on organic compounds and their role in life processes.

Many modern, high-tech materials are at least partially composed of organic compounds . Organic chemists spend much of their time creating new compounds and developing better ways of synthesizing previously known compounds. Which Industries Hire Organic Chemists? Organic chemists at all levels are generally employed by pharmaceutical, biotech, chemical, consumer product, and petroleum industries. Chemists in industry mainly work in development, while chemists in academia are involved in more basic research. The federal (e.g., Food and Drug Administration , Patent and Trademark Office ) state, and local governments also hire organic chemists. Biotechnology Biotechnology (“biotech” for short) is a field of applied biology that involves using living organisms and bioprocesses to create or modify products for a specific use. The cultivation of plants has been viewed as the earliest example of biotechnology and the precursor to modern genetic engineering and cell and tissue culture technologies. Virtually all biotechnology products are the result of organic chemistry. Biotechnology is used in in health care, crop production and agriculture, nonfood uses of crops and other products (e.g., biodegradable plastics, vegetable oil, biofuels), and environmental applications.

Biotechnology Companies: These companies make products such as seeds for crops that are resistant to certain diseases, seed coatings with specific properties, and plants that are drought resistant. Chemical The chemical industry is crucial to modern world economies and works to convert raw materials such as oil, natural gas, air, water, metals, and minerals into more than 70,000 different products. These base products are then used to make consumer products in addition to manufacturing, service, construction, agriculture, and other industries. Over three-fourths of the chemical industry’s output worldwide is polymers and plastics. Chemicals are used to make a wide variety of consumer goods, as well as thousands of products that are inputs to the agriculture, manufacturing, construction, and service industries. The chemical industry itself consumes about a quarter of its own output. Major industrial customers include rubber and plastic products, textiles, apparel, petroleum refining, pulp and paper, and primary metals. Chemical companies: BASF , Bayer , Braskem , Celanese , Dow , DuPont , Eastman Consumer Products Consumer products companies make consumer products for everyday use, such as soaps, detergents, cleaning products, plastic goods, and cosmetics.

Consumer products companies: PPG Industries , DuPont , Mitsubishi Chemical , Johnson & Johnson Petroleum The petroleum industry includes the global processes of exploration, extraction, refining, transporting, and marketing petroleum products. The largest volume products of the industry are fuel oil and gasoline. Petroleum is also the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics. The industry is usually divided into three major components: upstream (exploration and production), midstream (transportation), and downstream (refining crude oil, processing and purifying natural gas, creating petrochemicals). Petroleum companies: ExxonMobil , Shell Chemicals , Chevron Phillips Chemial Company , BP Pharmaceutical The pharmaceutical industry develops, produces, and markets drugs licensed for use as medications for humans or animals. Some pharmaceutical companies deal in brand-name (i.e., has a trade name and can be produced and sold only by the company holding the patent) and/or generic (i.e., chemically equivalent, lower-cost version of a brand-name drug) medications and medical devices (agents that act on diseases without chemical interaction with the body).

Pharmaceuticals (brand name and generic) and medical devices are subject to a large number of country-specific laws and regulations regarding patenting, testing, safety assurance, efficacy, monitoring, and marketing. Pharmaceuticals companies: The ACS Division of Organic Chemistry What Is the Difference Between Organic and Inorganic? What Is the Difference Between Organic and Inorganic? Organic Versus Inorganic Benzene is an example of an organic compound. Benzene is made of carbon atoms bonded to other carbon atoms and to hydrogen atoms. Laguna Design / Getty Images Updated September 29, 2016. Question: What Is the Difference Between Organic and Inorganic? Organic compounds and inorganic compounds form the basis for chemistry. Here is a look at the difference between organic and inorganic compounds, plus examples of each type. Answer: The primary difference between organic compounds and inorganic compounds is that organic compounds always contain carbon while most inorganic compounds do not contain carbon. Also, almost all organic compounds contain carbon-hydrogen or C-H bonds. Note, containing carbon is not sufficient for a compound to be considered organic! Examples of Organic Compounds or Molecules Molecules associated with living organisms are organic.

These include nucleic acids, fats, sugars, proteins, enzymes and hydrocarbon fuels. DNA table sugar or sucrose, C12H22O11 benzene, C6H6 Chemical Reactivity Chemical Reactivity Chemical Reactivity Organic chemistry encompasses a very large number of compounds ( many millions ), and our previous discussion and illustrations have focused on their structural characteristics. Now that we can recognize these actors ( compounds ), we turn to the roles they are inclined to play in the scientific drama staged by the multitude of chemical reactions that define organic chemistry. We begin by defining some basic terms that will be used frequently as this subject is elaborated. Chemical Reaction: A transformation resulting in a change of composition, constitution and/or configuration of a compound ( referred to as the reactant or substrate ). Reactant or Substrate: The organic compound undergoing change in a chemical reaction. Other compounds may also be involved, and common reactive partners ( reagents ) may be identified. The reactant is often ( but not always ) the larger and more complex molecule in the reacting system. Most ( or all ) of the reactant molecule is normally incorporated as part of the product molecule. Reagent: A common partner of the reactant in many chemical reactions.

It may be organic or inorganic; small or large; gas, liquid or solid. The portion of a reagent that ends up being incorporated in the product may range from all to very little or none. Product(s) The final form taken by the major reactant(s) of a reaction. Reaction Conditions The environmental conditions, such as temperature, pressure, catalysts & solvent, under which a reaction progresses optimally. Catalysts are substances that accelerate the rate ( velocity ) of a chemical reaction without themselves being consumed or appearing as part of the reaction product. Catalysts do not change equilibria positions. Chemical reactions are commonly written as equations: Reaction Classification Classifying Organic Chemical Reactions If you scan any organic textbook you will encounter what appears to be a very large, often intimidating, number of reactions. These are the "tools" of a chemist, and to use these tools effectively, we must organize them in a sensible manner and look for patterns of reactivity that permit us make plausible predictions. Most of these reactions occur at special sites of reactivity known as functional groups , and these constitute one organizational scheme that helps us catalog and remember reactions.

Ultimately, the best way to achieve proficiency in organic chemistry is to understand how reactions take place, and to recognize the various factors that influence their course. This is best accomplished by perceiving the reaction pathway or mechanism of a reaction. 1. Classification by Structural Change First, we identify four broad classes of reactions based solely on the structural change occurring in the reactant molecules. This classification does not require knowledge or speculation concerning reaction paths or mechanisms. The letter R in the following illustrations is widely used as a symbol for a generic group. It may stand for simple substituents such as H– or CH3–, or for complex groups composed of many atoms of carbon and other elements. Four Reaction Classes Rearrangement In an addition reaction the number of σ-bonds in the substrate molecule increases, usually at the expense of one or more π-bonds. The reverse is true of elimination reactions, i.e.the number of σ-bonds in the substrate decreases, and new π-bonds are often formed. Substitution reactions, as the name implies, are characterized by replacement of an atom or group (Y) by another atom or group (Z). Aside from these groups, the number of bonds does not change.

A rearrangement reaction generates an isomer, and again the number of bonds normally does not change. The examples illustrated above involve simple alkyl and alkene systems, but these reaction types are general for most functional groups, including those incorporating carbon-oxygen double bonds and carbon-nitrogen double and triple bonds. Some common reactions may actually be a combination of reaction types. The reaction of an ester with ammonia to give an amide, as shown below, appears to be a substitution reaction ( Y = CH3O & Z = NH2 ); however, it is actually two reactions, an addition followed by an elimination. The addition of water to a nitrile does not seem to fit any of the above reaction types, but it is simply a slow addition reaction followed by a rapid rearrangement, as shown in the following equation. Rapid rearrangements of this kind are called tautomerizations. Additional examples illustrating these classes of reaction may be examined by Clicking Here 2. Classification by Reaction Type At the beginning, it is helpful to identify some common reaction types that will surface repeatedly as the chemical behavior of different compounds is examined. This is not intended to be a complete and comprehensive list, but should set the stage for future elaborations.

Acidity and Basicity It is useful to begin a discussion of organic chemical reactions with a review of acid-base chemistry and terminology for several reasons. First, acid-base reactions are among the simplest to recognize and understand. Second, some classes of organic compounds have distinctly acidic properties, and some other classes behave as bases, so we need to identify these aspects of their chemistry. Finally, many organic reactions are catalyzed by acids and/or bases, and although such transformations may seem complex, our understanding of how they occur often begins with the functioning of the catalyst. Organic chemists use two acid-base theories for interpreting and planning their work: the Brønsted theory and the Lewis theory. Brønsted Theory According to the Brønsted theory, an acid is a proton donor, and a base is a proton acceptor. In an acid-base reaction, each side of the equilibrium has an acid and a base reactant or product, and these may be neutral species or ions. H-A + B:(–) (acid1) (base1) (base2) (acid2) Structurally related acid-base pairs, such as {H-A and A:(–)} or {B:(–) and B-H} are called conjugate pairs.

Substances that can serve as both acids and bases, such as water, are termed amphoteric. H-Cl + H2O (base) (acid) (acid) (base) The relative strength of a group of acids (or bases) may be evaluated by measuring the extent of reaction that each group member undergoes with a common base (or acid). Water serves nicely as the common base or acid for such determinations. Thus, for an acid H-A, its strength is proportional to the extent of its reaction with the base water, which is given by the equilibrium constant Keq. H-A + H2O H3O(+) + A:(–) Since these studies are generally extrapolated to high dilution, the molar concentration of water (55.5) is constant and may be eliminated from the denominator. The resulting K value is called the acidity constant, Ka. Clearly, strong acids have larger Ka's than do weaker acids. Because of the very large range of acid strengths (greater than 1040), a logarithmic scale of acidity (pKa) is normally employed. Stronger acids have smaller or more negative pKa values than do weaker acids.

Some useful principles of acid-base reactions are:  The stronger the acid the weaker its conjugate base; the stronger the base the weaker its conjugate acid.  Acid-base equilibria always favor the weakest acid and the weakest base. Examples of Brønsted Acid-Base Equilibria Acid-Base Reaction 10-34 34 In all the above examples water acts as a common base. The last example ( NH3 ) cannot be measured directly in water, since the strongest base that can exist in this solvent is hydroxide ion. Consequently, the value reported here is extrapolated from measurements in much less acidic solvents, such as acetonitrile. Since many organic reactions either take place in aqueous environments ( living cells ), or are quenched or worked-up in water, it is important to consider how a conjugate acid-base equilibrium mixture changes with pH. A simple relationship known as the Henderson-Hasselbalch equation provides this information. When the pH of an aqueous solution or mixture is equal to the pKa of an acidic component, the concentrations of the acid and base conjugate forms must be equal ( the log of 1 is 0 ).

If the pH is lowered by two or more units relative to the pKa, the acid concentration will be greater than 99%. On the other hand, if the pH ( relative to pKa ) is raised by two or more units the conjugate base concentration will be over 99%. Consequently, mixtures of acidic and non-acidic compounds are easily separated by adjusting the pH of the water component in a two phase solvent extraction. For example, if a solution of benzoic acid ( pKa = 4.2 ) in benzyl alcohol ( pKa = 15 ) is dissolved in ether and shaken with an excess of 0.1 N sodium hydroxide ( pH = 13 ), the acid is completely converted to its water soluble ( ether insoluble ) sodium salt, while the alcohol is unaffected. The ether solution of the alcohol may then be separated from the water layer, and pure alcohol recovered by distillation of the volatile ether solvent. The pH of the water solution of sodium benzoate may then be lowered to 1.0 by addition of hydrochloric acid, at which point pure benzoic acid crystallizes, and may be isolated by filtration.

For a discussion of how acidity is influenced by molecular structure Click Here . Basicity The basicity of oxygen, nitrogen, sulfur and phosphorus compounds or ions may be treated in an analogous fashion. Thus, we may write base-acid equilibria, which define a Kb and a corresponding pKb. However, a more common procedure is to report the acidities of the conjugate acids of the bases ( these conjugate acids are often "onium" cations ). The pKa's reported for bases in this system are proportional to the base strength of the base. A useful rule here is: pKa + pKb = 14. We see this relationship in the following two equilibria: Acid-Base Reaction Basicity Constants Although it is convenient and informative to express pKa values for a common solvent system (usually water), there are serious limitations for very strong and very weak acids. Thus acids that are stronger than the hydronium cation, H3O(+), and weak acids having conjugate bases stronger than hydroxide anion, OH(–), cannot be measured directly in water solution. Solvents such as acetic acid, acetonitrile and nitromethane are often used for studying very strong acids.

Relative acidity measurements in these solvents may be extrapolated to water. Likewise, very weakly acidic solvents such as DMSO, acetonitrile, toluene, amines and ammonia may be used to study the acidities of very weak acids. For both these groups, the reported pKa values extrapolated to water are approximate, and many have large uncertainties. A useful table of pKa values in DMSO solution has been compiled from the work of F.G. Bordwell, and may be reached by Clicking Here . Lewis Theory According to the Lewis theory, an acid is an electron pair acceptor, and a base is an electron pair donor. Lewis bases are also Brønsted bases; however, many Lewis acids, such as BF3, AlCl3 and Mg2+, are not Brønsted acids. The product of a Lewis acid-base reaction, is a neutral, dipolar or charged complex, which may be a stable covalent molecule. As shown at the top of the following drawing, coordinate covalent bonding of a phosphorous Lewis base to a boron Lewis acid creates a complex in which the formal charge of boron is negative and that of phosphorous is positive.

In this complex, boron acquires a neon valence shell configuration and phosphorous an argon configuration. If the substituents (R) on these atoms are not large, the complex will be favored at equilibrium. However, steric hindrance of bulky substituents may prohibit complex formation. The resulting mixture of non-bonded Lewis acid/base pairs has been termed "frustrated", and exhibits unusual chemical behavior. Two examples of Lewis acid-base equilibria that play a role in chemical reactions are shown in equations 1 & 2 below. In the first example, an electron deficient aluminum atom bonds to a covalent chlorine atom by sharing one of its non-bonding valence electron pairs, and thus achieves an argon-like valence shell octet. Because this sharing is unilateral (chlorine contributes both electrons), both the aluminum and the chlorine have formal charges, as shown. If the carbon chlorine bond in this complex breaks with both the bonding electrons remaining with the more electronegative atom (chlorine), the carbon assumes a positive charge. We refer to such carbon species as carbocations. Carbocations are also Lewis acids, as the reverse reaction demonstrates.

Many carbocations (but not all) may also function as Brønsted acids. Equation 3 illustrates this dual behavior; the Lewis acidic site is colored red and three of the nine acidic hydrogen atoms are colored orange. In its Brønsted acid role the carbocation donates a proton to the base (hydroxide anion), and is converted to a stable neutral molecule having a carbon-carbon double bond. A terminology related to the Lewis acid-base nomenclature is often used by organic chemists. Here the term electrophile corresponds to a Lewis acid, and nucleophile corresponds to a Lewis base. Electrophile: An electron deficient atom, ion or molecule that has an affinity for an electron pair, and will bond to a base or nucleophile. Nucleophile: An atom, ion or molecule that has an electron pair that may be donated in bonding to an electrophile (or Lewis acid). To learn more about the relationship of basicity and nucleophilicity, and for examples of acid/base catalysis of organic reactions Click Here . Oxidation and Reduction Reactions A parallel and independent method of characterizing organic reactions is by oxidation-reduction terminology. Carbon atoms may have any oxidation state from –4 (e.g.

CH4 ) to +4 (e.g. CO2 ), depending upon their substituents. Fortunately, we need not determine the absolute oxidation state of each carbon atom in a molecule, but only the change in oxidation state of those carbons involved in a chemical transformation. To determine whether a carbon atom has undergone a redox change during a reaction we simply note any changes in the number of bonds to hydrogen and the number of bonds to more electronegative atoms such as O, N, F, Cl, Br, I, & S that has occurred. Bonds to other carbon atoms are ignored. This count should be conducted for each carbon atom undergoing any change during a reaction. If the number of hydrogen atoms bonded to a carbon increases, and/or if the number of bonds to more electronegative atoms decreases, the carbon in question has been reduced (i.e. it is in a lower oxidation state). If the number of hydrogen atoms bonded to a carbon decreases, and/or if the number of bonds to more electronegative atoms increases, the carbon in question has been oxidized (i.e. it is in a higher oxidation state).

If there has been no change in the number of such bonds, then the carbon in question has not changed its oxidation state. In the hydrolysis reaction of a nitrile shown above, the blue colored carbon has not changed its oxidation state. These rules are illustrated by the following four addition reactions involving the same starting material, cyclohexene. Carbon atoms colored blue are reduced, and those colored red are oxidized. In the addition of hydrogen both carbon atoms are reduced, and the overall reaction is termed a reduction. Peracid epoxidation and addition of bromine oxidize both carbon atoms, so these are termed oxidation reactions. Addition of HBr reduces one of the double bond carbon atoms and oxidizes the other; consequently, there is no overall redox change in the substrate molecule. For a discussion of how oxidation state numbers may be assigned to carbon atoms Click Here . Since metals such as lithium and magnesium are less electronegative than hydrogen, their covalent bonds to carbon are polarized so that the carbon is negative (reduced) and the metal is positive (oxidized). Thus, Grignard reagent formation from an alkyl halide reduces the substituted carbon atom.

In the following equation and half-reactions the carbon atom (blue) is reduced and the magnesium (magenta) is oxidized. 3. Classification by Functional Group Functional groups are atoms or small groups of atoms (usually two to four) that exhibit a characteristic reactivity when treated with certain reagents. To view a table of the common functional groups and their class names Click Here . A particular functional group will almost always display its characteristic chemical behavior when it is present in a compound. Because of this, the discussion of organic reactions is often organized according to functional groups. The following table summarizes the general chemical behavior of the common functional groups. For reference, the alkanes provide a background of behavior in the absence of more localized functional groups. Functional Class (Z = OR, Cl, NHR, etc.) Substitution (of Z); Substitution (of α–H) Addition (to C=O) This table does not include any reference to rearrangement, due to the fact that such reactions are found in all functional classes, and are highly dependent on the structure of the reactant. Furthermore, a review of the overall reaction patterns presented in this table discloses only a broad and rather non-specific set of reactivity trends.

This is not surprising, since the three remaining categories provide only a coarse discrimination (comparable to identifying an object as animal, vegetable or mineral). Consequently, apparent similarities may fail to reflect important differences. For example, addition reactions to C=C are significantly different from additions to C=O, and substitution reactions of C-X proceed in very different ways, depending on the hybridization state of carbon. Reaction Variables The Variables of Organic Reactions In an effort to understand how and why reactions of functional groups take place in the way they do, chemists try to discover just how different molecules and ions interact with each other as they come together. To this end, it is important to consider the various properties and characteristics of a reaction that may be observed and/or measured as the reaction proceeds . The most common and useful of these are listed below: 1. Reactants and Reagents A. Reactant Structure: Variations in the structure of the reactant may have a marked influence on the course of a reaction, even though the functional group is unchanged.

Thus, reaction of 1-bromopropane with sodium cyanide proceeds smoothly to yield butanenitrile, whereas 1-bromo-2,2-dimethylpropane fails to give any product and is recovered unchanged. In contrast, both alkyl bromides form Grignard reagents (RMgBr) on reaction with magnesium. B. Reagent Characteristics: Apparently minor changes in a reagent may lead to a significant change in the course of a reaction. For example, 2-bromopropane gives a substitution reaction with sodium methylthiolate but undergoes predominant elimination on treatment with sodium methoxide. 2. Product Selectivity A. Regioselectivity: It is often the case that addition and elimination reactions may, in principle, proceed to more than one product. Thus 1-butene might add HBr to give either 1-bromobutane or 2-bromobutane, depending on which carbon of the double bond receives the hydrogen and which the bromine. If one possible product out of two or more is formed preferentially, the reaction is said to be regioselective. Simple substitution reactions are not normally considered regioselective, since by definition only one constitutional product is possible.

However, rearrangements are known to occur during some reactions. B. Stereoselectivity: If the reaction products are such that stereoisomers may be formed, a reaction that yields one stereoisomer preferentially is said to be stereoselective. In the addition of bromine to cyclohexene, for example, cis and trans-1,2-dibromocyclohexane are both possible products of the addition. Since the trans-isomer is the only isolated product, this reaction is stereoselective. C. Stereospecificity: This term is applied to cases in which stereoisomeric reactants behave differently in a given reaction. Examples include: (i) Formation of different stereoisomeric products, as in the reaction of enantiomeric 2-bromobutane isomers with sodium methylthiolate, shown in the following diagram. Here, the (R)-reactant gives the configurationally inverted (S)-product, and (S)-reactant produces (R)-product. The (R) and (S) notations for configuration are described in a later section of this text.

(ii) Different rates of reaction, as in the base-induced elimination of cis & trans-4-tert-butylcyclohexyl bromide (equation 1 below). (iii) Different reaction paths leading to different products, as in the base-induced elimination of cis & trans-2-methylcyclohexyl bromide (equation 2 below). The mechanisms of these substitution and elimination reactions are discussed in the alkyl halide section of this text. 3. Reaction Characteristics A. Reaction Rates: Some reactions proceed very rapidly, and some so slowly that they are not normally observed. Among the variables that influence reaction rates are temperature (reactions are usually faster at a higher temperature), solvent, and reactant / reagent concentrations. Useful information about reaction mechanisms may be obtained by studying the manner in which the rate of a reaction changes as the concentrations of the reactant and reagents are varied. This field of study is called kinetics. B. Intermediates: Many reactions proceed in a stepwise fashion. This can be convincingly demonstrated if an intermediate species can be isolated and shown to proceed to the same products under the reaction conditions.

Some intermediates are stable compounds in their own right; however, some are so reactive that isolation is not possible. Nevertheless, evidence for their existence may be obtained by other means, including spectroscopic observation or inference from kinetic results. 4. Factors that Influence Reactions It is helpful to identify some general features of a reaction that have a significant influence on its facility. Some of the most important of these are: A. Energetics : The potential energy of a reacting system changes as the reaction progresses. The overall change may be exothermic ( energy is released ) or endothermic ( energy must be added ), and there is usually an activation energy requirement as well. Tables of Standard Bond Energies are widely used by chemists for estimating the energy change in a proposed reaction. As a rule, compounds constructed of strong covalent bonds are more stable than compounds incorporating one or more relatively weak bonds. B. Electronic Effects : The distribution of electrons at sites of reaction (functional groups) is a particularly important factor. Electron deficient species or groups, which may or may not be positively charged, are attracted to electron rich species or groups, which may or may not be negatively charged. We refer to these species as electrophiles & nucleophiles respectively.

In general, opposites attract and like repel. The charge distribution in a molecule is usually discussed with respect to two interacting effects: An inductive effect , which is a function of the electronegativity differences that exist between atoms (and groups); and a resonance effect , in which electrons move in a discontinuous fashion between parts of a molecule. C. Steric Effects : Atoms occupy space. When they are crowded together, van der Waals repulsions produce an unfavorable steric hindrance. Steric hindrance may influence conformational equilibria , as well as destabilizing transition states of reactions . D. Stereoelectronic Effects : In many reactions atomic or molecular orbitals interact in a manner that has an optimal configurational or geometrical alignment. Departure from this alignment inhibits the reaction. E. Solvent Effects : Most reactions are conducted in solution, not in a gaseous state. The solvent selected for a given reaction may exert a strong influence on its course. Remember, solvents are chemicals, and most undergo chemical reaction under the right conditions.

Reaction Mechanisms Mechanisms of Organic Reactions A detailed description of the changes in structure and bonding that take place in the course of a reaction, and the sequence of such events is called the reaction mechanism. A reaction mechanism should include a representation of plausible electron reorganization, as well as the identification of any intermediate species that may be formed as the reaction progresses. These features are elaborated in the following sections. 1. The Arrow Notation in Mechanisms Since chemical reactions involve the breaking and making of bonds, a consideration of the movement of bonding ( and non-bonding ) valence shell electrons is essential to this understanding. It is now common practice to show the movement of electrons with curved arrows, and a sequence of equations depicting the consequences of such electron shifts is termed a mechanism. In general, two kinds of curved arrows are used in drawing mechanisms: A full head on the arrow indicates the movement or shift of an electron pair: A partial head (fishhook) on the arrow indicates the shift of a single electron: The use of these symbols in bond-breaking and bond-making reactions is illustrated below.

If a covalent single bond is broken so that one electron of the shared pair remains with each fragment, as in the first example, this bond-breaking is called homolysis. If the bond breaks with both electrons of the shared pair remaining with one fragment, as in the second and third examples, this is called heterolysis. Bond-Breaking Bond-Making Other Arrow Symbols Chemists also use arrow symbols for other purposes, and it is essential to use them correctly. The Reaction Arrow The Basics of Organic Chemistry - dummies The Basics of Organic Chemistry The Basics of Organic Chemistry The Basics of Organic Chemistry When you explore biology, you’ll find that many processes are constantly occurring in living organisms. The study of organic chemistry — which focuses on carbon molecules — is central to all living organisms. The ability to convert ingested fuel to usable energy is what differentiates a living organism from a dead one. The ingested fuel contains a variety of large molecules (macromolecules) that get broken down. When the macromolecules have been broken down into their smallest parts, they can enter the cells, which contain more macromolecules, which are involved in more processes. What is organic chemistry? In organic chemistry, the focus is on the element carbon.

Carbon is central to all living organisms; however, thousands of nonliving things (such as drugs, plastics, and dyes) are made from carbon compounds. Diamonds are carbon atoms in a crystal structure. Diamonds are so hard because the atoms of carbon are so closely bonded together in the crystal form. That same ability to pack closely together makes carbon an excellent structural element in its other forms as well. One atom of carbon can combine with up to four other atoms. Therefore, organic compounds usually are large and can have several atoms and molecules bonded together. Organic molecules can be large, and they comprise the structural components of living organisms: carbohydrates, proteins, nucleic acids, and lipids. Carbon is key In their outer shells, carbon atoms have four electrons that can bond with other atoms. When carbon is bonded to hydrogen (which is common in organic molecules), the carbon atom shares an electron with hydrogen, and hydrogen likewise shares an electron with carbon. Carbon-hydrogen molecules are referred to as hydrocarbons. Nitrogen, sulfur, and oxygen also are often joined to carbon in living organisms. Long carbon chains = low reactivity Large molecules form when carbon atoms are joined together in a straight line or in rings.

The longer the carbon chain, the less chemically reactive the compound is. However, in biology, other measures of reactivity are used. One example is enzymatic activity, which refers to how much more quickly a certain molecule can allow a reaction to occur. One key to knowing that a compound is less reactive is that its melting and boiling points are high. Generally, the lower a compound’s melting and boiling points, the more reactive it is. For example, the hydrocarbon methane, which is the primary component of natural gas, has just one carbon and four hydrogen atoms. Because it is the shortest carbon compound, it has the lowest boiling point (-162°C) and is a gas at room temperature. It is highly reactive. On the other hand, a compound made of an extremely long carbon chain has a boiling point of 174°C (compared to water, which has a boiling point of 100°C). Because it takes so much more for it to boil, it is much less reactive and is not gaseous at room temperature. Forming functional groups based on properties In organic chemistry, molecules that have similar properties (whether they are chemical or physical properties) are grouped together.

The reason they have similar properties is because they have similar groups of atoms; these groups of atoms are called functional groups. Chemical properties involve one substance changing into another substance by reacting. An example of a chemical property is the ability of chlorine gas to react explosively when mixed with sodium. The chemical reaction creates a new substance, sodium chloride (table salt). Physical properties refer to different forms of a substance, but the substance remains the same; no chemical reaction or change to a new substance occurs. Some of the properties that the functional groups provide include polarity and acidity. For example, the functional group called carboxyl (-COOH) is a weak acid. Polarity refers to one end of a molecule having a charge (polar), and the other end having no charge (nonpolar). For example, the plasma membrane has hydrophilic heads on the outside that are polar, and the hydrophobic tails (which are nonpolar) form the inside of the plasma membrane.

Question: Which element is basic to all organic chemistry?
Answer: Carbon