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Chapter

Cover Biochemistry and Molecular Biology

Raising electrons of water back up the energy scale: photosynthesis  

This chapter explains how photosynthesis occurs in plant cell chloroplasts, noting that the part that is dependent on light is the splitting of water to generate NADPH. It describes chlorophyll, which is a green pigment that receives light energy and is present in the membrane of organelles called thylakoids. When activated by photons, chlorophyll molecules donate electrons to chains of electron carriers arranged in two photosystems: PSI and PSII. The chapter talks about the loss of the electrons by chlorophyll. This makes it a very powerful oxidizing agent, capable of accepting electrons from water in the water-splitting centre. Adenosine triphosphate (ATP) is generated by the chemiosmotic mechanism during the passage of electrons from one photosystem to the other.

Chapter

Cover Human Physiology

Introduction to the respiratory system  

This chapter analyses the energy needed by animals for normal activities. This is mainly derived from the oxidative breakdown of foodstuffs, particularly that of carbohydrates and fats. It discusses the process called internal or cellular respiration, wherein the mitochondria oxidize carbohydrates and fatty acids generate adenosine triphosphate (ATP). The oxygen needed for this energy metabolism is ultimately derived from the atmosphere by the process of external respiration, which also serves to eliminate the carbon dioxide produced by the cells. The chapter cites the key process of external respiration, which is gas exchange between the air deep in the lungs and the blood that perfuses them. In addition to their role in gas exchange, the lungs have a variety of non-respiratory functions such as their role in trapping blood-borne particles.

Book

Cover Protecting Group Chemistry
Protecting Group Chemistry provides an overview of the general methods that are used to block the reactivity of—i.e. protect—specific functional groups, thus allowing others, present within the same molecule, to be manipulated unambiguously. An introductory chapter outlines protecting group strategy, relevant aspects of functional group reactivity, temporary protection, and introduces the concept of protecting group devices as an aid to unifying the wide range of available methods. The rest of the book is divided on the basis of broad classes of the experimental conditions that lead to cleavage of each protecting group (acid/electrophile, base/nucleophile, oxidising or reducing agent).

Chapter

Cover Making the Transition to University Chemistry

The Halogens  

This chapter discusses the halogens, also known as either Group 17 or Group VII. It also notes the exception of featuring astatine due to its high radioactivity. The physical properties of the halogens range between the melting points, boiling points, atomic radius, ionic radius, electronegativity, ionization energy, and dispersion forces. Additionally, the oxidizing ability of the halogens decreases in positivity, while the reducing ability of the halide ions increases. Fluorine is known to be exceptionally strongly oxidizing. Aqueous halide ions are tested by adding aqueous silver nitrate acidified with dilute nitric acid. An equilibrium is set up when chlorine dissolves in water.

Chapter

Cover Making the Transition to University Chemistry

Transition Metals 1  

This chapter discusses the halogens, also known as either Group 17 or Group VII. It also notes the exception of featuring astatine due to its high radioactivity. The physical properties of the halogens range between the melting points, boiling points, atomic radius, ionic radius, electronegativity, ionization energy, and dispersion forces. Additionally, the oxidizing ability of the halogens decreases in positivity, while the reducing ability of the halide ions increases. Fluorine is known to be exceptionally strongly oxidizing. Aqueous halide ions are tested by adding aqueous silver nitrate acidified with dilute nitric acid. An equilibrium is set up when chlorine dissolves in water.

Chapter

Cover Protecting Group Chemistry

Redox deprotection  

This chapter focuses on redox deprotection. Oxidation-labile protecting groups offer a means of releasing functional groups under essentially neutral conditions which is useful when hydrolytic deprotection is not tolerated and silyl protecting groups are unsuitable. In particular, a CH2 group that links a functional group to an electron-rich aromatic ring is prone to oxidation giving a hemiacetal, which is unstable with respect to aldehyde formation, and release of the functional group. Some oxidising agents activate the CH2 towards nucleophilic attack by water in a process equivalent overall to abstraction of hydride ion. The chapter then looks at internal redox processes, including free-radical deprotection, protecting group interchange, and photochemical deprotection. It also considers reductive methods, including hydrogenolysis.