Question

Draw structures of and supply names for the organic compounds produced by reacting ethene with each of the following substances. \(\begin{array}{ll}{\text { a. water }} & {\text { c. hydrogen chloride }} \\\ {\text { b. hydrogen }} & {\text { d. fluorine }}\end{array}\)

Short answer

The organic compounds produced by reacting ethene with each of the following substances are: a. Water: Structure: CH3CH2OH Name: Ethanol b. Hydrogen: Structure: CH3CH3 Name: Ethane c. Hydrogen chloride: Structure: CH3CH2Cl Name: Chloroethane d. Fluorine: Structure: CH2FCH2F Name: 1,2-difluoroethane

Step-by-step solution

a. Reaction with Water

Ethene reacts with water through an electrophilic addition reaction, in the presence of an acid catalyst (usually sulphuric acid). This reaction produces ethanol (C2H5OH). The ethene molecule has a double bond between its two carbon atoms, the water molecule adds across this double bond, breaking it, and forming a single bond to each of the carbon atoms. Structure: CH3CH2OH Name: Ethanol

b. Reaction with Hydrogen

When ethene reacts with hydrogen in the presence of a metal catalyst like palladium or platinum, it undergoes a hydrogenation reaction. This is categorized as an addition reaction, in which the double bond between the carbon atoms of ethene is broken, and a hydrogen atom is added to each of those carbons. This forms ethane (C2H6). Structure: CH3CH3 Name: Ethane

c. Reaction with Hydrogen Chloride

Ethene reacts with hydrogen chloride (HCl) through an electrophilic addition mechanism. The double bond of ethene attracts the partially positively charged hydrogen atom, and the electron pair from the carbon-carbon double bond moves toward the hydrogen atom. This breaks the double bond and results in the formation of a new bond between the hydrogen atom and one of the carbon atoms in ethene, while the chloride ion forms a new bond with the other carbon. The resulting compound is chloroethane (C2H5Cl). Structure: CH3CH2Cl Name: Chloroethane

d. Reaction with Fluorine

When ethene reacts with fluorine (F2), it undergoes an addition reaction similar to its reaction with the hydrogen halides. The electron-rich double bond of ethene attracts the fluorine atoms, which have a partial positive charge. This breaks the double bond and allows two fluorine atoms to form new bonds with the carbons of ethene. The resulting compound is 1,2-difluoroethane (C2H4F2). Structure: CH2FCH2F Name: 1,2-difluoroethane

Key concepts

Electrophilic Addition Reaction

Electrophilic addition reactions are a cornerstone of organic chemistry, especially when dealing with alkenes—the carbon-carbon double bond-containing compounds. This type of reaction occurs when an electrophile, an atom or molecule attracted to electrons, approaches the electron-rich double bond of the alkene. In our exercise, ethene serves as a prime example, being the simplest alkene.

The pivotal moment is when the double bond, a pair of electrons shared between the carbons, acts as a magnet to the electrophile. In the steps provided, various electrophiles split the double bond to form two new bonds, each joining to one of the carbon atoms of the original alkene. The reaction with water, known as hydration, forms ethanol, and the reaction with hydrogen chloride forms chloroethane. Both reflect classic electrophilic addition, showcasing the versatility and predictability of this organic transformation.

Hydrogenation of Alkenes

Hydrogenation is akin to giving alkenes a hydrogen embrace—the addition of hydrogen to double bonds, transforming them into single bonds. It’s a specific type of electrophilic addition and is particularly useful in industries to convert oils into fats, such as in the production of margarine from vegetable oil.

In the textbook exercise, ethene's carbon-carbon double bond is hydrogenated using a metal catalyst such as palladium or platinum, which facilitates the addition of hydrogen atoms. This is akin to turning a pair of dancers (the double bond) into solo performers (single bonds), joining hands with new partners (hydrogen atoms) on each side, resulting in the extremely stable ethane. This reaction's subtleties and its dependency on catalysts are crucial for students seeking a thorough understanding of alkene reactions.

Halogenation of Alkenes

Halogenation is like a chemistry dance where alkenes waltz with halogens, like chlorine or fluorine, to form dihalogenated products. This addition reaction is notable for its textbook precision and predictability—each carbon from the broken double bond gains a new halogen dance partner.

In our step-by-step solutions, we see ethene reacting with fluorine to produce 1,2-difluoroethane. Here, each carbon atom of the ethene gets its own fluorine atom, resulting in a molecule where friendly neighbors (the carbon atoms) now hold hands with twins (the fluorine atoms). The term '1,2' in the name highlights the position of the fluorine atoms on the carbon chain, an essential aspect of organic chemistry nomenclature that indicates the structure of the molecule.

Organic Chemistry Nomenclature

In organic chemistry, nomenclature is the formal system for naming compounds—it’s like the address and the name tag for each molecule, outlining its family (functional groups) and its place of residence (position on the carbon chain). It employs semi-systematic methods that ensure each compound has a unique and descriptive name.

The names given in the textbook solutions, such as ethanol and chloroethane, are shaped by IUPAC rules, the universally agreed language for chemical naming. These names sleekly communicate the number of carbons, the type of carbon-carbon bonds, and the identities of any substituents attached to them. For instance, the 'eth' prefix signals a two-carbon backbone, while the suffixes like '-ol' and '-ane' tell us about the functional groups—alcohols and alkanes, respectively. Learning to decipher and compose these names is like mastering an essential vocabulary that will empower students to fluently converse in the language of organic chemistry.