Organic Chemistry Topic 11

What is Organic Chemistry? The study of carbon and most carbon compounds “The chemistry of life” … but includes far more compounds than those made by living things.

Bonding of Carbon Atoms Carbon can form so many compounds because carbon atoms easily form covalent bonds with other carbon atoms Can be single, double, or triple covalent bonds

Bonding of Carbon Atoms Lewis Dot Diagram of Carbon in ground state Lewis dot diagram of bonded carbon atom Enables four covalent bonds Tetrahedral shape Angles are actually 109.50

Some Terminology Organic compounds containing only single bonds are said to be saturated. Organic compounds containing one or more double or triple bonds are called unsaturated compounds.

More Terminology Hydrocarbons - organic compounds that contain only hydrogen and carbon atoms Homologous series - group of related compounds in which each member differs from the one before by one additional unit. Alkanes Alkenes Alkynes

Chemistry Humor According to a chemist, why is the world so diverse? Because it's made up of alkynes of people.

Alkanes All single bonds between carbon atoms Therefore, all saturated. As the number of carbon atoms in this homologous series increases, so does the boiling point Names end with “-ane”

Alkanes Methane - Natural gas Ethane - Also natural gas Propane - outdoor grills/home heating Butane - lighters Pentane, Hexane, Heptane, Octane, Nonane, Decane - all found in gasoline Candle wax - 20 or more carbon atoms Road Tar - 40 or more carbon atoms

General Formula For Alkanes Each successive carbon adds two more hydrogen atoms Let’s develop a general formula for alkanes… CnH2n+2

Alkenes Each member of alkene series contains one double covalent bond Names are same as for alkanes, except change ending to “-ene”. Ethene - (common name “ethylene”) Unsaturated

Alkenes Let’s develop a general formula for “alkenes”…. CnH2n

Alkynes Contain one triple bond between carbon atoms Names are same as for alkanes, except change ending to “-yne”. Ethyne (common name “acetylene” - used in welding torches)

Alkynes Let’s develop a general formula for alkynes CnH2n-2 Pull out Reference Tables… Table P - Organic Prefixes Table Q - homologous series & general formulas

Homework Review Book Page 197 #1-18.

Let’s Keep some terms straight… Molecular formula - represents the actual atoms in a molecule Reminder - empirical formula is the simplest integer ratio in which atoms combine in a compound. Structural Formula - attempts to show the kinds and numbers of atoms, but also the bonding patterns and approximate shapes Condensed structural formulas

Let’s Keep some terms straight… Ball-and-stick model Space-filling model (very similar to “molecular shape” model)

Isomers Get a model kit and build a ball-and-stick model of butane. How many carbons and hydrogen did you need? Use the same number of carbons and hydrogens, but build something different than the butane you built above.

Isomers Starting with butane there’s more than one way to combine the carbon and hydrogen atoms. When a molecular formula can be represented by more than one structural arrangement, the compounds are called isomers of one another.

Isomers Even though they have the same molecular formula, isomers have different chemical and physical properties. Different boiling points Different reactivities As the number of carbon atoms increases, so does the number of possible isomers.

Naming Organic Compounds When carbon atoms in one continuous chain, called a “straight chain” hydrocarbon Also called “normal form” The letter “n-” precedes the name of straight chain hydrocarbons

Naming Organic Compounds Compounds with branched chains must be given different names because they have different chemical and physical properties. Naming rules are governed by IUPAC (International Union of Pure and Applied Chemistry)

Naming Organic Compounds Step 1 - Find the longest continuous chain of carbon atoms The compound will be named based on its longest chain. For example, if the longest chain is 6, then the compound will be named as a hexane.

Naming Organic Compounds Step 2 - Identify attached Alkyl Groups An alkyl group contains one less hydrogen than an alkane with the same number of carbon atoms Step 3 - Assign numbers to the carbon atoms in the longest chain. They must be numbered from the end that will give the lowest number for the attached group.

Naming Organic Compounds Step 4 - Name the compound by stating the location of the attached chain, the alkyl group, then the main branch name

Naming Organic Compounds Some additional naming info… If there is more than one of the same type of group attached to the parent chain, then a prefix is used di- means two; tri- means three; tetra- means four Commas are used to indicate the specific carbon to which each group is attached

Naming Organic Compounds Worksheet - Isomers of octane Worksheet 25-4 Apply “A Compound Problem”

Functional Groups Functional Groups - are atoms or groups of atoms that replace hydrogen in a hydrocarbon, and give the compound distinctive chemical and physical properties.

Organic Acids Organic Acids are a homologous series Functional group is carboxyl group (-COOH) Name comes from corresponding hydrocarbon, but replace ending “-e” with “-oic acid” Ethanoic acid (common name “acetic acid”, which is found in vinegar)

Organic Acids Most organic compounds are nonelectrolytes, but organic acids are weak electrolytes. Reference Table R

Alcohols Alcohols - organic compounds where one hydrogen of a hydrocarbon is replaced by an -OH group (called a hydroxyl group) The -OH group resembles the hydroxide ion, but it isn’t the same. It doesn’t form hydroxide ion in water. Therefore, alcohols are nonelectrolytes

Alcohols The hydroxyl group is polar, though, which allows alcohols to dissolve in water. Name by changing corresponding alkane ending “-e” to “-ol”

Esters Esters are organic compounds whose type formula is R-CO-ORI Part comes from an organic acid, and the RI part comes from an alcohol Esters have strong, fragrant odors.

Esterification Esterification - The organic reaction between an organic acid and an alcohol to produce an ester plus water. Esters are named by using the alkyl name of the alcohol followed by the acid group modified to end in “-oate”.

Esterification Esterification Lab

More About Alcohols There are several different types of alcohols Type depends on number of hydroxyl groups Type depends on the position of each hydroxyl group on the chain

Alcohols Alcohols are primary, secondary, or tertiary based on whether the hydroxyl group is attached to a primary, secondary, or tertiary carbon atom. Primary carbon - attached to only one other carbon atom Secondary Carbon - attached to two other carbon atoms Tertiary Carbon - attached to three other carbon atoms

Alcohols Primary Alcohol - has a hydroxyl group attached to primary carbon Secondary Alcohol - hydroxyl group attached to secondary carbon Tertiary Alcohol - hydroxy group attached to tertiary alcohol

Alcohols Monohydroxy alcohols - have one hydroxyl group Dihydroxy alcohols - two hydroxyl groups 1,2 ethanediol Trihydroxy Alcohols- three hydroxyl groups 1,2,3 propanetriol

Some Practice Page 204 #34,35, 39, 41, 42, 43,45

Organic Halides (“Halocarbons”) When a halogen (F, Cl, Br, or I) replaces a hydrogen on an alkane, the compound is called an organic halide (or halocarbon). The functional group is the attached halogen. Named by citing the location of the halogen attached to the chain.

Ethers Series of organic compounds in which two carbon chains are joined together by an oxygen atom bonded between two carbon atoms. Named using alkyl group names followed by “ether”.

Worksheet 26-1 Apply Halocarbon, Alcohol, or Ether?

Amines Amines are formed when one of the hydrogens of ammonia is replaced by an alkyl group. Named by taking the alkane name and change the ending “-e” to “-amine”, and number the alkane chain to show the location of the amine group.

Carbonyl Group When an oxygen is bound to a carbon by a double bond, it is called a carbonyl group. Overhead “Functional Groups of Organic Compounds”

Aldehydes Aldehydes are organic compounds in which the carbonyl group is on the end carbon Named by substituting “-al” for the final “-e” of the corresponding alkane name. Methanal’s common name is “formaldehyde”

Ketones Ketones formed when carbonyl group is attached to an interior carbon atom that is attached to two other carbon atoms. Named by replacing final “-e” of corresponding alkane name with “-one” Propanone’s common name is “acetone” - nail polish remover. Ketones are often used as solvents (because both polar and nonpolar

Amino Acids Amino acids contain the carboxylic group (-COOH) and an amine. The amine group is attached to the carbon adjacent to the acid group. Amino acids are the building blocks of protein. The body must take in (ingest) 10 essential amino acids, because the body can’t produce them. The remaining amino acids can be synthesized.

Amides Amides are compounds formed by combination of two amino acids. Look at Figure 11-15 page 166. Also called a “peptide bond”. Additional amino acids can be linked, forming “polypeptides”, and eventually, proteins.

Saponification The name of the organic reaction that makes soap. An ester reacts with an inorganic base to produce an alcohol and soap.

Polymerization Polymers - organic compounds made up of chains of smaller units covalently bonded together The formation of these large polymer molecules is called polymerization

Polymerization Each individual unit is called a monomer. Synthetic Plastics (nylon, rayon, polyethylene, etc..) are polymers

Polymerization Two General Types of Polymerization Reactions Addition Polymerization - involves the joining of monomers of unsaturated compounds Condensation Polymerization - result from the bonding of monomers by removing water from hydroxyl groups and joining the monomers by an ester or ether linkage.

Addition Polymerization An addition reaction is one in which two or more molecules join together to give a single product. During the polymerisation of ethene, thousands of ethene molecules join together to make poly(ethene) - commonly called polyethylene. The number of molecules joining up is very variable, but is in the region of 2000 to 20000.

Addition Polymerization The mechanism The over-all process is known as free radical addition. Chain initiation The chain is initiated by free radicals, Ra, produced by reaction between some of the ethene and the oxygen initiator. Chain propagation Each time a free radical hits an ethene molecule a new longer free radical is formed. etc

Substitution Reactions A substitution reaction involves the replacement of one or more of the hydrogen atoms in a saturated hydrocarbon with another atom or group. CH4 + Cl2  CH3Cl + HCl

Substitution Reactions If a mixture of methane and chlorine is exposed to a flame, it explodes - producing carbon and hydrogen chloride. This isn't a very useful reaction! So how does the substitution reaction occur without an explosion?

Substitution Reaction The mechanism involves a chain reaction. The chain is initiated (started) by UV light breaking a chlorine molecule into free radicals. Cl2  2Cl• By the way, this is an example of a photochemical reaction.

Substitution Reaction Chain propagation reactions - these are the reactions that keep the chain going… CH4 + Cl• CH3• + HCl CH3• + Cl2  CH3Cl + CL• The chain terminates when one of these reactions occurs… 2Cl•  Cl2 CH3•  +  Cl•  CH3Cl CH3•  +  CH3•  CH3CH3

Addition Reactions Addition Reactions involve adding one or more atoms at a double or triple bond. C2H4 + Cl2  C2H4Cl2 Or C2H4 + H2  C2H6

Fermentation Fermentation is a chemical process in which yeast cell secrete enzymes (zymase) and break sugar chains into carbon dioxide and water C6H12O6  2C2H5OH + 2CO2