Carbon bonding in organic chemistry

The aldol reaction is one of the oldest and important methods for the construction of carbon-carbon bonds in organic chemistry. A classic aldol reaction is the reaction of two carbonyl compounds, or a carbonyl electrophile with an enol nucleophile, to form a new /3-hydroxy carbonyl compound. The first report was appeared in 1872 (1,2), and later in nearly 140 years, new and powerful variants of these classical aldol reactions, such as Mukaiyama aldol reactions, vinylogous aldol reactions, and reductive aldol reactions, and so on have been developed as one of the most versatile and reliable carbon-carbon bond-forming reactions in the syntheses of many important natural occurring or synthetic molecules (3-6). There now exists a large amount of literature documenting different aspects of aldol reactions, and the stable increasing is predictable. 

Although there are many higher-order classifications in chemistry such as functional groups or types of carbon bonding in organic chemistry, as a rule they cannot be combined hierarchically. There may even be competing classifications of the same feature, as in the case of acids. Should we call Brpnsted-Lowry and Lewis acids two models of one natural kind or two alternative natural kinds having their own context of application ... 

The aldol reaction is one of the oldest and most important methods for the construction of carbon-carbon bonds in organic chemistry (17), and numerous organocatalytic reactions target this important transformahon. 

First reported in 1838, the aldol reaction has remained one of the most powerful tools for the formation of carbon-carbon bonds in organic chemistry. In order to induce diastereoselectivity in an aldol transformation, both enolate geometry and facial selectivity must be controlled. Oxazolidinone auxiliaries facilitate control over both of these parameters. By varying the Lewis aeid in oxazolidinone controlled aldol reaetions, both 1,2-syn and 1,2-anti stereoehemistries can be obtained. ... 

For a review of 1,3-dipolar addition to other double bonds, see Bianchi De Micheli Gandolfi, in Patai, Ref. 1. pt. 1, pp. 369-532. For a review of such addition to the C=S bond, see Dunn Rudorf Carbon Disulfide in Organic Chemistry Wiley New York, 1989, pp. 97-119. 

Double bond In organic chemistry, the combination of two carbon atoms by two valencies (C=C). The double bonds are the prerequisite for curing of polymerization adhesives. 

A bond is a pair of electrons shared by the two atoms it holds together. There are many types of chemical bonds including hydrogen, ionic and covalent bonds. In organic chemistry (based on the element carbon) we deal mainly with covalent bonds, which may occur as single, double or triple bonds. 

Reduction (Section 2 19) Gam in the number of electrons as sociated with an atom In organic chemistry reduction of carbon occurs when a bond between carbon and an atom which IS more electronegative than carbon is replaced by a bond to an atom which is less electronegative than carbon Reductive ami nation (Section 22 10) Method for the prepara tion of amines in which an aldehyde or a ketone is treated with ammonia or an amine under conditions of catalytic hy drogenation... 

Since the six carbons shown above have 10 additional bonds, the variety of substituents they carry or the structures they can be a part of is quite varied, making the Diels-Alder reaction a powerful synthetic tool in organic chemistry. A moment s reflection will convince us that a molecule like structure [XVI] is monofunctional from the point of view of the Diels-Alder condensation. If the Diels-Alder reaction is to be used for the preparation of polymers, the reactants must be bis-dienes and bis-dienophiles. If the diene, the dienophile, or both are part of a ring system to begin with, a polycyclic product results. One of the first high molecular weight polymers prepared by this synthetic route was the product resulting from the reaction of 2-vinyl butadiene [XIX] and benzoquinone [XX] ... 

The most important interatomic bond in polymers, and indeed in organic chemistry, is the covalent bond. This is formed by the sharing of one or more pairs of electrons between two atoms. An example is the bonding of carbon and hydrogen to form methane Figure 5.2). 

The polarity of covalent bonds between carbon and substituents is the basis of important structure-reactivity relationships in organic chemistry. The effects of polar bonds are generally considered to be transmitted in two ways. Successive polarization through bonds is called the inductive fect. It is expected that such an effect would diminish as the number of intervening bonds increases. 

One more hybridization scheme is important in organic chemistry. It is called sp hybridization and applies when carbon is directly bonded to two atoms, as in acetylene. The structure of acetylene is shown in Figure 2.18 along with its bond distances and bond angles. Its most prominent feature is its linear geometr-y. 

Alkenes are hydrocarbons that contain a carbon-carbon double bond. A carbon-carbon double bond is both an important structural unit and an important functional group in organic chemistry. The shape of an organic molecule is influenced by the presence of this bond, and the double bond is the site of most of the chemical reactions that alkenes undergo. Some representative alkenes include isobutylene (an industrial chemical), a-pinene (a fragrant liquid obtained from pine trees), and famesene (a naturally occuning alkene with three double bonds). 

The addition of the a-carbon of an enolizable aldehyde or ketone 1 to the carbonyl group of a second aldehyde or ketone 2 is called the aldol reaction It is a versatile method for the formation of carbon-carbon bonds, and is frequently used in organic chemistry. The initial reaction product is a /3-hydroxy aldehyde (aldol) or /3-hydroxy ketone (ketol) 3. A subsequent dehydration step can follow, to yield an o ,/3-unsaturated carbonyl compound 4. In that case the entire process is also called aldol condensation. 

The terms primary- secondary, tertiary, and quaternary are routinely used in organic chemistry, and their meanings need to become second nature. For example, it we were to say, "Citric acid is a tertiary alcohol," we would mean that it has an alcohol functional group (-OH) bonded to a carbon atom that is itself bonded to three other carbons. (These other carbons may in turn connect to other functional groups). 

In organic chemistry, an oxidation is a reaction that causes a decrease in electron density on carbon, either by bond formation between carbon and a more electronegative atom (usually oxygen, nitrogen, or a halogen) or by bond-breaking... 

It appears here with all of the hydrogens showing. In pictures of the structural formulas in organic chemistry, carbon atoms and hydrogen atoms typically aren t shown because the picture would just be too crowded. A carbon atom is implied whenever a line ends or whenever one line joins another. Hydrogens are assumed to connect to any carbon that has a free bond. (Carbon can form four bonds, so if only three are showing, the other is attached to a hydrogen.)... 

---