Organic chemistry and unit reactions

Author: Chief Editor: Ma Hongfei et al.
Publisher:
Publish Date: 1997-11-01
Features:
Content Summary This book is compiled based on the basic requirements of teaching reform by the Ministry of Education. It includes organic chemistry, organic unit reactions and intermediates, and organic processes. The book is divided into 18 chapters. After explaining the basic theories, it introduces the mechanisms, influencing factors, and practical applications of major unit reactions, and discusses various synthetic routes and processes of specific products. With the aim of cultivating applied talents, the book selects materials appropriately, focuses on fundamental theories, integrates organic processes, and emphasizes applications. It can serve as a textbook for chemistry, chemical engineering, environmental protection, and related disciplines in ordinary universities and colleges, and can also be referenced by scientific and technical personnel engaged in fine chemical, organic synthesis, and production.
Excerpt:
Chapter 1 Introduction
Section 1 Organic Compounds and Organic Chemistry
Organic chemistry is the science that studies the structure, properties, and synthesis of organic compounds. What are organic compounds? Organic compounds are carbon-containing compounds, in addition to carbon, they also contain elements such as hydrogen, oxygen, nitrogen, sulfur, phosphorus, and halogens. The main components of organic compounds are carbon and hydrogen. Structurally, hydrocarbons can be considered the parent body of organic compounds, while other organic compounds are derivatives of hydrocarbons. Therefore, organic compounds can also be defined as hydrocarbons and their derivatives. By derivatives, we mean compounds formed by replacing one or more hydrogen atoms in hydrocarbons with other atoms or groups. The elements composing organic compounds are not many, but the number of organic compounds is astonishing, exceeding 5 million. Inorganic compounds involve elements throughout the periodic table but only have about 400,000 to 500,000 types. There is no clear absolute boundary between organic and inorganic compounds. However, some carbon-containing compounds with typical inorganic properties, such as CO, CO?, and carbonates, are not included in organic compounds. Why are they called organic compounds? Because, over a century ago, organic compounds were obtained from living organisms, unlike inorganic compounds derived from non-living minerals. Therefore, in 1806, the renowned chemist Berzelius first called compounds obtained from living organisms "organic compounds." At that time, chemists believed that only living organisms could create organic matter because they possessed "vitality." This vitalistic theory constrained people's thinking and hindered scientific progress. In 1828, the German chemist W?hler synthesized the organic compound urea from the typical inorganic compound potassium cyanate and ammonium chloride (reaction equation see below), demonstrating that inorganic substances could be transformed into organic substances in the laboratory without relying on the mysterious "vitality." This discovery dealt a powerful blow to the vitalistic theory. Subsequently, countless organic compounds were synthesized, including highly complex proteins and nucleic acids, marking the era of synthesis in organic chemistry. Today, of course, no one still believes in the pessimistic vitalistic theory, but due to historical and habitual reasons, the term "organic" is still retained.
Section 2 Characteristics of Organic Compounds
There is no clear boundary between organic and inorganic compounds, so why is organic chemistry studied as an independent discipline? This is because organic compounds have common characteristics distinct from typical inorganic compounds.
1. Complex molecular composition and vast number Why are there so many organic compounds? This is mainly because the main atom in organic compounds—carbon—has a strong ability to combine. Carbon atoms can form stable covalent bonds, link into straight chains, branched chains, and rings, and form single, double, and triple bonds, thereby creating a variety of complex molecules. In organic compounds, isomerism occurs, where the same molecular formula can result in different compounds due to different connections between atoms in the molecule or different spatial arrangements of atoms.
2. Certain differences in properties between organic and inorganic compounds
(1) Easily combustible Most organic compounds are easily combustible. For example, gasoline, alcohol, sugar, and edible vegetable oils are highly flammable. This is mainly due to the presence of carbon and hydrogen in organic compounds, whereas inorganic compounds are generally non-flammable.
(2) Low melting point Even organic compounds with relatively high melting points rarely exceed 400°C, while solid inorganic compounds generally have melting points of around 1000°C. This is because the crystals of inorganic compounds are maintained by strong electrostatic forces between ions, resulting in high lattice energy. In organic compounds, intermolecular arrangements depend on weak electrostatic attractions (Van der Waals forces), and intermolecular forces are weaker, so melting points are lower.
(3) Instability to heat Compared to inorganic compounds, organic compounds are generally less thermally stable and decompose easily when heated. Many organic compounds begin to decompose at temperatures of 200–300°C, while inorganic compounds are generally heat-resistant.
(4) Insolubility in water Most chemical bonds in organic compounds are covalent bonds, which are generally weakly polar or non-polar. According to the principle "like dissolves like," organic compounds are insoluble or poorly soluble in highly polar water but dissolve easily in non-polar or weakly polar organic solvents. However, some highly polar organic compounds, such as low-molecular-weight alcohols, carboxylic acids, and sulfonic acids, are also soluble in water. Organic solvents are commonly used when dissolving organic compounds.
(5) Slow reaction rates Most reactions in organic compounds are intermolecular reactions, which often require a certain amount of energy (activation energy). Therefore, many organic compound reactions are slow, taking several hours, dozens of hours, or even longer to complete. Heating, pressurization, stirring, adding catalysts, or exposure to light are often used to accelerate reactions. However, some organic compounds react very quickly, even explosively.
(6) Complex reactions and varied products During organic reactions, side reactions often occur. The main reaction is the primary reaction of the compound, while others are side reactions. Because organic compounds are complex molecules composed of many atoms, when they react with a reagent, all parts of the molecule may be affected, and after the reaction, a complex mixture of difficult separation is often produced, significantly reducing the yield of the main product. Therefore, if an organic compound reaction achieves a theoretical yield of 60–70%, it is considered relatively satisfactory. In industrial production, selecting favorable reaction conditions to reduce side reactions and increase the yield of the main product is one of the important tasks for engineering and technical personnel.