ORGANIC CHEMISTRY

1. ORGANIC CHEMISTRY

2. Naming Saturated Hydrocarbons • The International Union of Pure and Applied Chemistry (IUPAC) names for the first 12 "straight-chain" or "normal" alkanes are:

3. Alkanes and Cycloalkanes • The simplest saturated hydrocarbons are called alkanes. • Methane, CH4, is the simplest alkane. • The alkanes form a homologous series. • Each member of the series differs by a specific number and kind of atoms.

4. Alkanes and Cycloalkanes • The alkanes differ from each other by a CH2 or methylene group. • All alkanes have this general formula. CnH2n+2 • For example ethane, C2H6 , and propane, C3H8 , are the next two family members.

5. Alkanes and Cycloalkanes • Isomers are chemical compounds that have the same molecular formulas but different structures. • Two alkanes have the molecular formula C4H10. • They are a specific type of isomer called structural isomers. • Branched-chain alkanes are named by the following rules. • Choose the longest continuous chain of carbon atoms which gives the basic name or stem.

6. Naming Saturated Hydrocarbons • Number each carbon atom in the basic chain, starting at the end that gives the lowest number to the first group attached to the main chain (substituent). • For each substituent on the chain, we indicate the position in the chain (by an Arabic numeric prefix) and the kind of substituent (by its name). • The position of a substituent on the chain is indicated by the lowest number possible. • The number precedes the name of the substituent.

7. Naming Saturated Hydrocarbons • When there are two or more substituents of a given kind, use prefixes to indicate the number of substituents. • di = 2, tri = 3, tetra = 4, penta = 5, hexa = 6, hepta = 7, octa = 8, and so on. • The combined substituent numbers and names serve as a prefix for the basic hydrocarbon name. • Separate numbers from numbers by commas and numbers from words by hyphens. • Words are "run together".

8. Naming Saturated Hydrocarbons • Alkyl groups (represented by the symbol R) are common substituents. • Alkyl groups are fragments of alkanes in which one H atom has been removed for the connection to the main chain. • Alkyl groups have the general formula CnH2n+1. • In alkyl groups the -ane suffix in the name of the parent alkane is replaced by -yl. • A one carbon group is named methyl. • A two carbon group is named ethyl. • A three carbon group is named propyl. • Three alkanes have the formula C5H12. • There are three structural isomers of pentane.

9. Alkanes and Cycloalkanes • There are five isomeric hexanes, C6H14. • The number of structural isomers increases rapidly with • increasing numbers of carbon atoms. • The boiling points of the alkanes increase with molecular weight.

10. Alkanes and Cycloalkanes • Cyclic saturated hydrocarbons are called cycloalkanes. • They have the general formula CnH2n. • Some examples are:

11. Alkenes • The three classes of unsaturated hydrocarbons are: • alkenes and cycloalkenes, CnH2n • alkynes and cycloalkynes, CnH2n-2 • aromatic hydrocarbons • The simplest alkenes contain one C=C bond per molecule. • The general formula for simple alkenes is CnH2n. • The first two alkenes are: • ethene, C2H4 • and propene, C3H6 • Each doubly bonded C atom is sp2 hybridized. • The sp2 hybrid consists of: • two s bonds (single bonds) and • one s and one p bond (double bond)

12. Alkenes • The systematic naming system for alkenes uses the same stems as alkanes. • In the IUPAC system, the -ane suffix for alkanes is changed to -ene. • Common names for the alkenes have the same stem but use the suffix -ylene is used. • In chains of four or more C atoms, a numerical prefix shows the position of the lowest-numbered doubly bonded C atom. • Always choose the longest chain that contains the C=C bond. • Polyenes contain two or more double bonds per molecule. • Indicate the number of double bonds with suffixes: • -adiene for two double bonds. • -atriene for three double bonds, etc. • The positions of the substituents are indicated as for alkanes. • The position of the C=C bond(s) is/are given the lowest number(s) possible.

13. Cycloalkenes • Cycloalkenes have the general formula CnH2n-2. • Examples are: • cyclopentene • cyclohexene

14. Alkynes • Alkynes contain CC bonds. • The simplest alkyne is C2H2, ethyne, or acetylene. • Alkynes with only one C  C bond have the formula CnH2n-2. • Each carbon atom in a C  C bond is sp hybridized. • Each sp hybrid contains two  bonds and two  bonds. • The carbon atom will have one single bond and one triple bond. • Alkynes are named like the alkenes except that the suffix -yne is used with the characteristic stem • The alkyne stem is derived from the name of the alkane with the same number of carbon atoms.

15. Hydrocarbons: A Summary

16. Aromatic Hydrocarbons • Historically, aromatic was used to describe pleasant smelling substances. • Now it refers to benzene, C6H6,and derivatives of benzene. • Other compounds that have similar chemical properties to benzene are also called aromatic. • The structure of benzene, C6H6, is: • Coal tar is the common source of benzene and many other aromatic compounds. • Some aromatic hydrocarbons that contain fused rings are: • napthalene

17. Resonance in Benzene • C6H6 has two resonance structures with alternating double bonds. • The π electrons are delocalized over the ring. • C–C single bond = 154 pm • C=C bond = 134 pm • CC bonds in benzene = 139 pm π electrons delocalized

18. Other Aromatic Hydrocarbons • Many aromatic hydrocarbons contain alkyl groups attached to benzene rings (as well as to other aromatic rings). • The positions of the substituents on benzene rings are indicated by the prefixes: • ortho- (o-) for substituents on adjacent C atoms • meta- (m-) for substituents on C atoms 1 and 3 • para- (p-) for substituents on C atoms 1 and 4

19. Organic Halides • A halogen atom may replace almost any hydrogen atom in a hydrocarbon. • The functional group is the halide (-X) group. • Examples include: • chloroform, CHCl3 • 1,2-dichloroethane, ClCH2CH2Cl • para-dichlorobenzene

20. Alcohols and Phenols • The functional group in alcohols and phenols is the hydroxyl (-OH) group. • Alcohols and phenols can be considered derivatives of hydrocarbons in which one or more H atoms have been replaced by -OH groups. • Phenols are derivatives of benzene in which one H has been replaced by replaced by -OH group. • The stem for the parent hydrocarbon plus an -ol suffix is the systematic name for an alcohol. • A numeric prefix indicates the position of the -OH group in alcohols with three or more C atoms. • Common names are the name of the appropriate alkyl group plus alcohol.

21. Alcohols and Phenols • Ethyl alcohol (ethanol), C2H5OH, is the most familiar alcohol. H H O H H C C H H • Phenol, C6H5OH, is the most familiar phenol.

22. Alcohols and Phenols • Alcohols can be classified into three classes: • Primary (1°) alcohols like ethanol have the -OH group attached to a C atom that has one bond to another C atom. • Secondary(2°) alcohols have the –OH group attached to a C atom that has bonds to 2 other C atoms. • For example,2-propanol: • Tertiary (3°) alcohols have the –OH group attached to a C atom that is bonded to 3 other C atoms. • For example, 2-methyl-2-propanol

23. Alcohols and Phenols • Alcohols are named using the stem for the parent hydrocarbon plus an -ol suffix in the systematic nomenclature. • A numeric prefix indicates the position of the -OH group in alcohols with three or more C atoms. • Common alcohol names are the name of the appropriate alkyl group plus the word alcohol.

24. Alcohols and Phenols • There are several isomeric monohydric acyclic (contains no rings) alcohols that contain more than three C atoms. • There are four isomeric four-carbon alcohols.

25. Alcohols and Phenols • There are eight isomeric five-carbon alcohols.

26. Alcohols and Phenols • Polyhydric alcohols contain more than one -OH group per molecule.

27. Alcohols and Phenols • Phenols are usually called by their common (trivial) names.

28. Ethers • Ethers may be thought of as derivatives of water in which both H atoms have been replaced by alkyl or aryl groups. • Ethers are not very polar and not very reactive. • They are excellent solvents. • Common names are used for most ethers.

29. Aldehydes and Ketones • The functional group in aldehydes and ketones is the carbonyl group.

30. Aldehydes and Ketones • Except for formaldehyde, aldehydes have one H atom and one organic group bonded to a carbonyl group. • Ketones have two organic groups bonded to a carbonyl group.

31. Aldehydes and Ketones • Common names for aldehydes are derived from the name of the acid with the same number of C atoms. • IUPAC names are derived from the parent hydrocarbon name by replacing -e with -al.

32. Aldehydes and Ketones • The IUPAC name for a ketone is the characteristic stem for the parent hydrocarbon plus the suffix -one. • A numeric prefix indicates the position of the carbonyl group in a chain or on a ring.

33. Amines • Amines are derivatives of ammonia in which one or more H atoms have been replaced by organic groups (aliphatic or aromatic or a mixture of both). • There are three classes of amines.

34. Carboxylic acids contain the carboxyl functional group. The general formula for carboxylic acids is: R represents an alkyl or an aryl group Carboxylic Acids • IUPAC names for a carboxylic acid are derived from the name of the parent hydrocarbon. • The final -e is dropped from the name of the parent hydrocarbon • The suffix -oic is added followed by the word acid. • Many organic acids are called by their common (trivial) names which are derived from Greek or Latin.

35. Carboxylic Acids

36. Carboxylic Acids • Positions of substituents on carboxylic acid chains are indicated by numeric prefixes as in other compounds • Begin the counting scheme from the carboxyl group carbon atom. • They are also often indicated by lower case Greek letters. •  = 1st C atom •  = 2nd C atom •  = 3rd C atom, etc.

37. Nomenclature of Carboxylic Acids • Dicarboxylic acids contain two carboxyl groups per molecule.

38. Carboxylic Acids • Aromatic acids are usually called by their common names. • Sometimes, they are named as derivatives of benzoic acid which is considered to be the "parent" aromatic acid.

39. Some Derivatives of Carboxylic Acids

41. Isomerism • Isomers have identical composition but different structures • Two forms of isomerism • Constitutional (or structural) • Stereoisomerism • Constitutional • Same empirical formula but different atom-to-atom connections • Stereoisomerism • Same atom-to-atom connections but different arrangement in space.

42. Structural Isomers

43. Stereoisomers: Geometric Cis-2-butene Trans-2-butene Geometric isomers can occur when there is a C=C double bond.

44. Stereoisomers: Optical • Optical isomers are molecules with non-superimposable mirror images. • Such molecules are called CHIRAL • Pairs of chiral molecules are enantiomers. • Chiral molecules in solution can rotate the plane of plane polarized light. • Chirality generally occurs when a C atom has 4 different groups attached. Lactic acid

45. Chirality: Handedness in Nature These molecules are non-superimposable mirror images.

46. Sugars: Related to Alcohols • Sugars are carbohydrates, compounds with the formula Cx(H2O)y. What is the difference between a and b D-glucose?

47. Sucrose and Ribose Deoxyribose, the sugar in the DNA backbone.

48. Fats and Oils R = organic group with NO C=C bonds C12 = Lauric acid C16 = Palmitic acid C18 = Stearic acid What is the functional group in a fat or oil? R = organic group with C=C bonds C18 = oleic acid

49. Fats and Oils C=C bond Fats with C=C bonds are usually LIQUDS Oleic acid: a monounsaturated fatty acid

50. Trans Fatty Acids C=C bond • Oleic acid is a mono–unsaturated cis-fatty acid • Trans fatty acids have deleterious health effects. • Trans fatty acids raise plasma LDL cholesterol and lower HDL levels.