Presentation on theme: "Chapter 23 Functional Groups. Functional Groups Most organic chemistry involves substituents, which are groups attached to hydrocarbon chains. The substituents."— Presentation transcript:
Chapter 23 Functional Groups
Functional Groups Most organic chemistry involves substituents, which are groups attached to hydrocarbon chains. The substituents of organic molecules often contain oxygen, nitrogen, sulfur and phosphorus. They are called functional groups because they are the chemically functional parts of the molecules. Organic compounds can be classified according to their functional groups. They symbol R represents any carbon chains or rings attached to the functional group. And bonds of alkenes and alkynes are chemically reactive and are also considered functional groups.
Halogen Substituents alkyl halides Halocarbons in which a halogen is attached to a carbon of an aliphatic chain are called alkyl halides. The number of carbon atoms attached to the alkyl group determines whether the carbon is primary, secondary, or tertiary. aryl halides. Halocarbons in which a halogen is attached to a carbon of an arene (aromatic hydrocarbon) ring are called aryl halides. The attractions between halocarbon molecules are primarily the result of weak van der Waals interactions called dispersion forces. The attractions increase with the degree of halogen substitution.
Halogen Substituents The more highly halogenated organic compounds have higher boiling points. Very few halocarbons are found in nature, but they can be readily prepared and used for many purposes. Hydrofluorocarbons are used as refrigerants in automobile air conditioning systems. Halothan (2-bromo-2-chloro-1,1,1,-trifluoroethane) is used and an anesthetic.
CH 3 CH 2 CH 3 CH 3 CH 2 F CH 3 CH 2 OH Molecular weight Boiling point, °C Effect of Structure on Boiling Point
CH 3 CH 2 CH 3 Molecular weight Boiling point, °C Intermolecular forces are weak. Only intermolecular forces are induced dipole-induced dipole attractions. Effect of Structure on Boiling Point
CH 3 CH 2 F Molecular weight Boiling point, °C Dipole moment, D A polar molecule; therefore dipole-dipole and dipole-induced dipole forces contribute to intermolecular attractions. Effect of Structure on Boiling Point
CH 3 CH 2 OH Molecular weight Boiling point, °C Dipole moment, D Highest boiling point; strongest intermolecular attractive forces. Hydrogen bonding is stronger than other dipole-dipole attractions. Effect of Structure on Boiling Point
Name the alkyl group and the halogen as separate words (alkyl + halide) Nomenclature of Alkyl Halides CH 3 F CH 3 CH 2 CH 2 CH 2 CH 2 Cl CH 3 CH 2 CHCH 2 CH 2 CH 3 Br Methyl fluoride Pentyl chloride 1-Ethylbutyl bromideCyclohexyl iodide H I
Name as halo-substituted alkanes. Number the longest chain containing the halogen in the direction that gives the lowest number to the substituted carbon. Nomenclature of Alkyl Halides CH 3 CH 2 CH 2 CH 2 CH 2 F CH 3 CHCH 2 CH 2 CH 3 Br 1-Fluoropentane 3-Iodopentane 2-Bromopentane CH 3 CH 2 CHCH 2 CH 3 I
Nomenclature of Alkyl Halides Halogen and alkyl groups are of equal rank when it comes to numbering the chain. Number the chain in the direction that gives the lowest number to the group (halogen or alkyl) that appears first. CH 3 Cl CH 3
1,2 or 1,3 or 1,4-dichlorobenzene chlorobenzene chloromethylbenzene benzyl chloride Aryl Halides
Alcohols and alkyl halides are classified as primary secondary tertiary according to their "degree of substitution." Degree of substitution is determined by counting the number of carbon atoms directly attached to the carbon that bears the halogen or hydroxyl group. Classification
Substitution Reactions Organic reactions often proceed more slowly than inorganic reactions. Organic reactions commonly involve the breaking of relatively strong covalent bonds. Catalysts are often needed. Many organic reactions are complex, often producing a mixture of products. The desired product must then be separated by distillation, crystallization, or other means. substitution reaction A common type of organic reaction is a substitution reaction, in which an atom or a group of atoms replaces another atom or group of atoms.
Substitution Reactions A halogen can replace a hydrogen atom on an alkane to produce a halocarbon. CH 4 + Cl 2 CH 3 Cl + HCl Sunlight or another source of ultraviolet radiation usually serves as a catalyst. Even under controlled conditions, this simple halogenation reaction produces a mixture of mono-, di-, tri-, and tetrachloromethanes.
Substitution Reactions Iron compounds are often used as catalysts for aromatic substitution reactions. Halogens on carbon chains are readily displace by hydroxide ions to produce an alcohol and a salt. CH 3 I + KOH CH 3 OH + KI
Substitution Reactions Iron compounds are often used as catalysts for aromatic substitution reactions. Halogens on carbon chains are readily displace by hydroxide ions to produce an alcohol and a salt. CH 3 I + KOH CH 3 OH + KI Fluoro groups are not easily displaced. Thus, fluorocarbons are seldom, if ever, used to make alcohols.
Questions How are organic compounds classified? According to their functional groups What is a halocarbon? Class of organic compounds containing covalently bonded fluorine, chlorine, bromine, or iodine. How can a halocarbon be prepared? By reacting an alkane with a halogen, catalyzed by UV light.
Questions Identify the functional group in each structure Isopropyl chloride hydroxyl CH 3 – CH 2 – NH 2 amino CH 3 – CH 2 – CH 2 – Br Halogen CH 3 – CH 2 – O – CH 2 – CH 3 ether
Questions Give the structural formula for the compound Isopropyl chloride CH 3 | CH 3 – C – Cl | H
Questions Give the structural formula for the compound 1-iodo-2,2-dimethylpentane CH 3 | I – CH 2 – C – CH 2 – CH 2 –CH 3 | CH 3
Questions Give the structural formula for the compound P-bromotoluene Write the names of all possible dichloropropanes that could form from the chlorination of propane. 1,1,-dichloropropane 1,2-dichloropropane 2,2-dichloropropane 1,3-dichloropropane
Questions Write the structural formulas for ethene, ethyl chloride, and ethanol. Identify their functional groups. Choose two of the compounds to illustrate a substitution reaction. Explain the terms primary, secondary and tertiary.
End of Section 23.1
Alcohols The –OH functional group in alcohols is called a hydroxyl group. Aliphatic alcohols can be classified into structural categories according to the number of R groups attached to the carbon with the hydroxyl group. PrimarySecondary Tertiary
Naming Alcohols - IUPAC When using the IUPAC system to name continuous-chain substituted alcohols, drop the –e ending of the parent alkane name and add the ending –ol. The parent alkane is the longest continuous chain of C that includes the C attached to the hydroxyl group. In numbering the longest continuous chain, the position of the hydroxyl group is given the lowest possible number. Alcohols containing two, three, and four – OH substituents are name diols, triols, and tetrols, respectively..
Common Names - Alcohol The alkyl group ethyl, for example, is named and followed by the word alcohol, as in ethyl alcohol. Compounds with more than one – OH substituent are called glycols. Methanol Methyl alcohol Common names of aliphatic alcohols are written in the same way as those of the halocarbons. Ethanol Ethyl alcohol 2-propanol Propyl alcohol
Properties of Alcohols Alcohols are capable of intermolecular hydrogen bonding. Therefore, they boil at higher temperatures than alkanes and halocarbons containing comparable numbers of atoms. Because alcohols are derivatives of water, (the hydroxyl group is part of a water molecule) they are somewhat soluble. Alcohols of up to four carbons are soluble in water in all proportions. The solubility of alcohols with four or more carbons in the chain is usually much lower.
Properties of Alcohols Alcohols consist of two parts: the carbon chain and the hydroxyl group. The carbon chain is nonpolar and is not attracted to water. The hydroxyl group is polar and strongly interacts with water through hydrogen bonding. For alcohols of up to four carbons, the polarity of the hydroxyl group is more significant than the nonpolarity of the carbon chain. These alcohols are soluble in water. As the number of carbon atoms increases above four, the nonpolarity of the chain becomes more significant, and the solubility decreases.
Properties of Alcohols Many aliphatic alcohols are used in laboratories, clinics and industry as rubbing alcohol, antiseptic and as a base for perfumes, creams, lotions and other cosmetics. Ethylene glycol (1,2-ethanediol) is the principal ingredient of certain antifreezes. Ethyl alcohol is called grain alcohol and is an important industrial chemical. Most ethanol is still produced by yeast fermentation of sugar. Fermentation is the production of ethanol from sugars by the action of yeast or bacteria.
Properties of Alcohols Ethanol is the intoxication substance in alcoholic beverages. It is a depressant and can be fatal if taken in large doses at once. The ethanol used in industrial application is denatured. Denatured alcohol is ethanol with an added substance to make it toxic. The added substance is often methyl alcohol, which is sometimes called wood alcohol because it used to be prepared by the distillation of wood. Wood alcohol is extremely toxic. As little as 10 mL has been reported to cause permanent blindness and as little as 30 mL to can cause death.
Addition Reactions The carbon-carbon single bonds in alkanes are not easy to break. In alkenes one of the bonds in the double bond is somewhat weaker and is easier to break than a carbon- carbon single bond. It is sometimes possible for a compound of general structure X-Y to add to a double bond. addition reaction In an addition reaction, a substance is added at the double or triple bond of an alkene or alkyne.
Addition Reactions Addition reactions of alkenes are an important method of introducing new functional groups into organic molecules. In alkenes one of the bonds in the double bond is somewhat weaker and is easier to break than a carbon- carbon single bond. It is sometimes possible for a compound of general structure X-Y to add to a double bond. addition reaction In an addition reaction, a substance is added at the double or triple bond of an alkene or alkyne.
Addition Reactions hydration reaction The addition of water to an alkene is a hydration reaction. Hydration reactions usually occur when the alkene and water are heated to about 100ºC in the presence of a trace of strong acid. (The acid usually HCl or H 2 SO 4, serves as a catalyst for the reaction.) When the reagent is a halogen, a disubstituted halocarbon is produced.
Addition Reactions The addition of bromine to carbon-carbon multiple bonds is often used as a chemical test for unsaturation in an organic molecule. Bromine has a brownish-orange color, but most organic compounds of bromine are colorless. The loss of the orange color is a positive test for unsaturation. If the orange remains, the sample is completely saturated.
Hydrogenation Reactions Hydrogen halides can also be added to a double bond. The product is called a monosubstituted halocarbon because it only has one substituent. hydrogenation reaction. The addition of hydrogen to a carbon-carbon double bond to produce an alkane is called a hydrogenation reaction. Hydrogenation reactions usually require a catalyst. Platinum or paladium are often used. The manufacture of margarine from unsaturated vegetable oils is a common application of a hydrogenation reaction.
Hydrogenation Reactions The hydrogenation of a double bond is a reduction reaction. Ethene is reduced to ethane. Under normal conditions, benzene resists hydrogenation. It also resists the addition of a halogen or a hydrogen halide. Under condition of high temperature and high pressures of hydrogen, and with certain catalysts, three molecules of hydrogen gas can reduce one molecule of benzene to form one molecule of cyclohexane.
Ethers An ether is a compound in which oxygen is bonded to two carbon groups. The general structure of an ether is R – O – R. The alkyl groups attached to the ether linkage are named in alphabetical order and are followed by the word ether. Some ethers are non-symmetric, because the R groups attached to the ether oxygen are different. H H H | | | H-C-O-C-C-H | | | H H H methyl ethyl ether
Ethers When both R groups are the same the ether is symmetric. Symmetric ethers are named using the prefix di-. Diethyl ether
Ethers Diethyl ether was the first reliable general anesthetic. Diethyl ether has been replaced by other anesthetics such as halothan because it is highly flammable and often causes nausea. Ethers usually have lower boiling points than alcohols of comparable molar mass. They have higher boiling points than comparable hydrocarbons and halocarbons. Ethers are more soluble in water than hydrocarbons and halocarbons, but less soluble than alcohols. This is because the O in an ether is a hydrogen acceptor. Ethers form more hydrogen bonds than hydrocarbons and halocarbons, but fewer than alcohols.
Questions How are alcohols classified and named? Alcohols are classified as primary, secondary, or tertiary. They are named by dropping the –e ending of the parent alkane name and adding the ending -0l How does the solubility of alcohols vary with the length of the carbon chains? Alcohols are soluble in water when the carbon chain of the alcohol contains four or fewer carbons. The solubility of longer chain alcohols is much lower. How can functional groups be introduced into organic molecules? By addition or substitution reactions