1-20 of 98 Results

  • Keywords: carbon x
Clear all

Chapter

Cover Oxidation and Reduction in Organic Synthesis

Oxidative cleavage reactions  

This chapter focuses on reactions which lead to the cleavage of carbon–carbon single (and multiple) bonds and the introduction of new bonds between carbon and an electronegative element, such as oxygen. It also considers the similar process which leads to the cleavage of bonds between carbon and other electropositive elements such as boron or silicon. The chapter begins by looking at the oxidative cleavage of carbon–carbon double bonds. Clipping an alkene to furnish two carbonyl compounds is most readily carried out with ozone (O3): the four substituents that were attached to the alkene end up as substituents on the two new carbonyl containing compounds. The chapter then studies the oxidative cleavage of carbon–carbon sigma bonds; of carbon–boron and carbon–silicon bonds; and of carbon–halogen bonds.

Chapter

Cover Oxidation and Reduction in Organic Synthesis

Reduction of carbon–carbon double and triple bonds  

This chapter addresses the reduction of carbon–carbon double and triple bonds. In particular, it examines ways of reducing multiple (π) bonds between carbon atoms by the addition of hydrogen (a process known as hydrogenation). The chapter begins by looking at the reduction of alkenes. Reaction of an alkene with hydrogen gas and one of the transition metal catalysts results in the reduction of the π-bond and formation of an alkene. The mechanism by which heterogeneous hydrogenation proceeds is complex and difficult to study as the reaction takes place on the surface of the metal, and the nature of this surface varies with the different catalysts used. The chapter then considers the reduction of alkynes and aromatic π-systems.

Chapter

Cover Organic Chemistry

What is organic chemistry?  

This chapter provides an overview of organic chemistry. Organic chemistry started as the chemistry of life, which was once thought to be different from the chemistry in the laboratory. Then it became the chemistry of carbon compounds, especially those found in coal. But now, it is both. It is the chemistry of the compounds formed by carbon and other elements such as those found in living things, in the products of living things, and other places where carbon is found. The chapter then looks at organic compounds before considering the relationship between organic chemistry and industry. It also presents the periodic table.

Chapter

Cover Plant Physiology and Development

Photosynthesis: The Light Reactions  

This chapter introduces the basic physical principles that underlie photosynthetic energy storage and the current understanding of the structure and function of the photosynthetic apparatus. It talks about how oxygenic photosynthetic organisms, such as plants, use solar energy to synthesize complex carbon compounds. It also explores the essential concepts that provide a foundation for understanding photosynthesis. The chapter also looks at light energy that drives the synthesis of carbohydrates and the generation of oxygen from carbon dioxide and water. It deals with the role of light in photosynthesis, the structure of the photosynthetic apparatus, and the processes that begin with the excitation of chlorophyll by light and culminate in the synthesis of ATP and NADPH.

Chapter

Cover Bioinorganic Chemistry

Metal– and metalloid–carbon bonds  

This chapter discusses the role of the transition metal-carbon bond in the activation of substrates such as carbon oxide, carbon dioxide, nitrogen, methane, alkenes, and alkynes, focusing in part on selected examples of metalloenzymes. It looks at the processing of organometal and -metalloid compounds in biogeochemical cycles. The chapter also explores the special role of adenosyl- and methyl-cobalamin (vitamin B12), the latter in the frame of the broad range of physiologically important methyl transfer reactions. Furthermore, it briefly sets out the physiological implications of the selenium-carbon bond. Lastly, the chapter addresses the biogeochemical making and breaking of the metal and -metalloid carbon bond in poisoning by, and detoxification of, mercury, lead, and arsenic.

Chapter

Cover Oxidation and Reduction in Organic Synthesis

Oxidation of activated carbon–hydrogen bonds  

This chapter evaluates the oxidation of activated carbon–hydrogen bonds. During the course of an oxidation, hydrogen can be removed in three ways, as either H+, H*, or H-. Normally, it is beneficial to have a functional group which stabilises the carbon left behind by such removal of hydrogen. As such, the chapter considers the hydrogen atom that is lost, activated by the functional group. It begins by looking at oxidation adjacent to oxygen. This is the most useful and widespread area of oxidation, as it encompasses the alcohol-aldehyde-carboxylic acid sequence which is used so often in synthesis. The chapter then studies oxidation adjacent to a carbon–carbon multiple bond, a carbonyl group, and nitrogen, as well as the oxidation of phenols and the formation of quinones.

Chapter

Cover Chemistry for the Biosciences

Hydrocarbons: the framework of life  

This chapter introduces organic chemistry, the chemistry of carbon and carbon-containing compounds. Carbon has an important structural role in organic compounds because of its high valency. Organic compounds have a simple hydrocarbon framework, to which are attached more specialized groups of atoms. The chapter then looks at the three different types of hydrocarbon: alkanes, which contain only single carbon–carbon bonds; alkenes, which contain at least one double carbon–carbon bond; and alkynes, which contain at least one triple carbon–carbon bond. A special hydrocarbon group is the aryl group, which is derived from an aromatic hydrocarbon by the removal of one or more hydrogen atoms. Finally, the chapter explores the physical and chemical properties of the hydrocarbons.

Book

Cover Mechanisms of Organic Reactions
Mechanisms of Organic Reactions begins with the modern concepts of organic chemical reactivity, then presents an up-to-date account of the mechanisms of major reactions of simple organic compounds. Each chapter leads from the experimental evidence to the mechanistic deductions, and ends with problems and a short bibliography. Chapter 1 presents a description and investigation of organic reaction mechanisms. The next chapter looks at nucleophilic substitution at saturated carbon. There follows a chapter on the elimination reactions to give alkenes. The fourth chapter covers reactions of nucleophiles with carbonyl compounds. The final chapter examines additions to carbon-carbon multiple bonds.

Chapter

Cover Human Physiology

The chemical constitution of the body  

This chapter describes the human body as consisting largely of four elements: oxygen, carbon, hydrogen, and nitrogen. It shows that about 70 percent of the lean body tissues is water, while the remaining 30 percent made up of organic material (i.e. molecules and minerals). The principal organic constituents of mammalian cells are the carbohydrates, fats, proteins, and nucleic acids, which are built from smaller molecules belonging to four classes of chemical compounds: sugars, fatty acids, amino acids, and nucleotides respectively. The chapter outlines the principal minerals found in tissues: calcium, phosphorus, potassium, and sodium. It gives an approximate indication of the chemical composition of the body for a young adult male, noting that there is individual variation and that the proportions of the various constituents vary between tissues and change during development.

Chapter

Cover Marine Ecology: Processes, Systems, and Impacts

Primary Production Processes  

This chapter introduces the major factors that control primary production and how to measure it. Primary production is the starting point of all life in marine systems. Primary producers in the oceans span many orders of magnitude. Production is measured using bottled incubations or, increasingly, from space, using (satellite-borne) ocean colour sensors that detect photosynthetic pigments in surface waters. The conversion of inorganic carbon into biomass, its subsequent sinking to the seabed, and sequestration over thousands of years are fundamental to an understanding of the ocean as a potential sink for increasing levels of atmospheric carbon dioxide. About 55% of the total carbon captured on Earth through the process of photosynthesis and production of biomass takes place in marine systems.

Chapter

Cover Oxidation and Reduction in Organic Synthesis

Reductive cleavage reactions  

This chapter studies reactions which completely cleave the bonds between carbon and electronegative elements, replacing them with bonds to hydrogen. It presents examples of reductions which cleave purely σ-bonds and also reactions which cleave both σ- and π-bonds. The chapter begins by looking at the reduction of carbon–nitrogen σ-bonds. Amines that are substituted with a benzyl group may be broken by reduction with hydrogen and a transition metal catalyst. Reductive cleavage using hydrogen and a catalyst is known as hydrogenolysis. The chapter then considers the reduction cleavage of carbon–oxygen bonds; reductive dehalogenation; reduction cleavage of carbon–sulfur bonds; and reductive cleavage of cyclopropane rings.

Chapter

Cover Oxidation and Reduction in Organic Synthesis

Reduction of carbon–heteroatom double and triple bonds  

This chapter explores the reduction of carbon–heteroatom double and triple bonds. There are many functional groups based on multiple bonds between carbon and either oxygen or nitrogen. The chapter demonstrates some of the corresponding reduction reactions of these functional groups. It begins by looking at the reduction of carbon–nitrogen π-bonds. Nitriles contain a strong triple bond between carbon and nitrogen. In terms of reactivity, nitriles are susceptible to nucleophilic attack and therefore reduction of these groups is easily effected by 'hydride' reducing agents. The chapter then considers the reduction of carbon–oxygen π-bonds. The reduction of aldehydes to primary alcohols and ketones to secondary alcohols is normally easy to accomplish using sodium borohydride or lithium aluminium hydride.

Chapter

Cover Pharmaceutical Chemistry

Carbohydrates and Carbohydrate Metabolism  

Alex White and Helen Burrell

This chapter focuses on carbohydrates, which are molecules composed almost exclusively of carbon, hydrogen, and oxygen. Carbohydrate monomers are called monosaccharides and are found throughout nature. The chapter explains how carbohydrates are synthesized in plants during the process of photosynthesis, with their carbon atoms being obtained from atmospheric carbon dioxide. The chapter considers carbohydrates as the main fuel source in human bodies and they are divided into two groups: simple sugars and complex carbohydrates. Simple sugars like glucose are metabolized directly via glycolysis and the citric acid cycle, whereas complex carbohydrates like starch and glycogen are first broken down into simple sugars.

Chapter

Cover Organic Chemistry

Atoms, Molecules, and Chemical Bonding—a Review  

This chapter presents an overview of organic chemistry and looks at the compounds of carbon. It argues that there are hugely more compounds of carbon than of all other elements combined. The chapter then discusses the special properties of the element, and the characteristics of the carbon atom. It begins the study of organic chemistry by reviewing the nature of atoms and, in particular, their electronic structures. The chapter also looks at valence electrons and ionic and covalent bonds. It then explains the method of representing atoms which gave prominence to their valence electrons and facilitated comparisons between different elements. The chapter then demonstrates the periodic table by looking at the Lewis representations of atoms. Finally, the chapter analyzes several scales to quantify electronegativity. It also considers bond polarity and an introduction to resonance.

Chapter

Cover Food and Sustainability

Energy  

Paul Behrens

This chapter focuses on the energy system, to investigate the ways in which energy is currently used in the food system and how this use may develop in the future. It outlines the physical nature of energy and power and describes the different sources of energy. The discussion highlights that food production uses around 15–20% of the total energy produced for human needs. The discussion covers two critical issues in energy use: the improved availability of energy in poorer countries and the implementation of low-carbon technologies in all countries. Furthermore, it explains the zero-carbon energy system. The chapter also explores how food systems can be decarbonized. Finally, it looks at the role agricultural systems could play in the energy transition itself.

Chapter

Cover Organic Synthesis

Retrosynthetic analysis I: The basic concepts  

This chapter discusses the basic concepts of retrosynthetic analysis. When presented with a specific target molecule, a synthetic route must be designed which enables a pure sample of the desired product to be obtained using a convenient and efficient procedure. Chemists have developed a logical approach for the design of routes for the preparation of organic compounds which involves working the synthesis backwards by making strategic carbon–carbon bond cleavages at points where, in the forward reaction, bond forming reactions may be achieved. This is known as either the disconnection approach or retrosynthetic analysis. The fundamentals of the process of retrosynthetic analysis may be demonstrated by consideration of the synthesis of the secondary alcohol.

Chapter

Cover Reactive Intermediates

Arynes  

This chapter describes arynes as neutral intermediates derived from aromatic rings by removing two substituents and leaving behind two electrons to be distributed between two orbitals. It highlights C6H4. This is based on benzene as the most common aryne, although aromatic and heteroaromatic systems can give similar species. The chapter also mentions that the need to postulate C6H4 started in the 1870s, which led to the formation of biphenyl in certain reactions. It was not until the 1940s that advanced clear and convincing arguments for the intermediacy of arynes were developed. The chapter analyzes ortho-Benzyne, which is usually represented as a singlet molecule with a carbon-carbon triple bond. It looks at theoretical calculations that support the view that the symmetrical triple bond structure is lowest in energy and suggests that the structure is distorted from benzene.

Chapter

Cover Organometallics 1

Alkylidene and alkylidyne complexes  

This chapter studies alkylidene and alkylidyne complexes. Whereas metal alkyl complexes have a long history, the first examples of compounds with metal–carbon double bonds were not discovered until 1964 by E. O. Fischer. These compounds have become known as carbene complexes. The metal is in a low oxidation state, and the bonding of the carbene ligand is reminiscent to that of carbon monoxide (CO). A second group of M=C compounds, with a highly oxidized metal centre, was subsequently discovered by R. R. Schrock and these are called alkylidene complexes. The chapter then considers complexes with metal–carbon triple bonds, as well as the reactivity of alkylidene and alkylidyne complexes and it also looks at dinuclear alkylidene and alkylidyne complexes.

Chapter

Cover Organonitrogen Chemistry

Enamines  

This chapter looks into imines. It enumerates the key features of imines: oxidation level two, susceptibility to nucleophilic attack on carbon, and easy protonation in relation to producing reactive iminium ions. Imines are prepared from the reaction of an aldehyde or a ketone with a primary amine. Thus, the reaction is driven primarily through the removal of water. Imine will be more stable than simple aliphatic imines if it is conjugated by an aromatic ring. The chapter discusses the reactions of imines through attack by carbon nucleophiles, the Vilsmeyer reaction, the Mannich reaction, reduction, and hydrolysis. Additionally, the chapter shows that the reduction to amines is readily achieved via hydrogenation of hydride reducing conditions.

Chapter

Cover Bifunctional Compounds

Allyl compounds  

This chapter focuses on allyl alcohols, which are renowned for their ease of oxidation. It refers to manganese dioxide, which is highly effective for bringing about the oxidation of primary allylic alcohols to the αβ-unsaturated aldehydes. It also describes a highly-selective oxidation of allylic alcohols that involves epoxidation of the carbon-carbon double bond using tert-butyl hydroperoxide and a titanium or vanadium catalyst. The chapter analyses a valuable method of asymmetric synthesis known as Sharpless epoxidation, which involves treating the allylic alcohol with tert-butyl hydroperoxide in the presence of titanium tetraisopropoxide and a chiral ester of tartaric acid. This produces epoxy alcohols, which can be converted into a wide variety of other products by reduction or nucleophilic addition. The chapter also covers allyl ethers and allyl halides.