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Organic Chemistry M. R. Naimi-Jamal Faculty of Chemistry Iran University of Science & Technology.

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1 Organic Chemistry M. R. Naimi-Jamal Faculty of Chemistry Iran University of Science & Technology

2 Chapter 2. Alkanes and Cycloalkanes Based on: McMurry’s Fundamental of Organic Chemistry, 4th edition, Chapter 2

3 3 Families of Organic Compounds Organic compounds can be grouped into families by their common structural features We shall survey the nature of the compounds in a tour of the families in this course This chapter deals with alkanes, compounds that contain only carbons and hydrogens, all connected exclusively by single bonds

4 4 2.1 Functional Groups Functional group - collection of atoms at a site within a molecule with a common bonding pattern The group reacts in a typical way, generally independent of the rest of the molecule For example, the double bonds in simple and complex alkenes react with bromine in the same way

5 5

6 6 Double Bond as Functional Group

7 7 Survey of Functional Groups Table 3.1 lists a wide variety of functional groups that you should recognize As you learn about them in each chapter it will be easier to recognize them The functional groups affect the reactions, structure, and physical properties of every compound in which they occur

8 8 Types of Functional Groups: Multiple Carbon–Carbon Bonds Alkenes have a C-C double bond Alkynes have a C-C triple bond Arenes (or aromatic hydrocarbons) have special bonds that are represented as alternating single and double C-C bonds in a six-membered ring

9 9 Multiple Carbon–Carbon Bonds

10 10 Functional Groups with Carbon Singly Bonded to an Electronegative Atom Alkyl halide: C bonded to halogen (C-X) Alcohol: C bonded O of a hydroxyl group (C-OH) Ether: Two C’s bonded to the same O (C-O-C) Amine: C bonded to N (C-N) Thiol: C bonded to SH group (C-SH) Sulfide: Two C’s bonded to same S (C-S-C) Bonds are polar, with partial positive charge on C (  +) and partial negative charge (  ) on electronegative atom

11 11

12 12 Groups with a Carbon–Oxygen Double Bond (Carbonyl Groups) Aldehyde: one hydrogen bonded to C=O Ketone: two C’s bonded to the C=O Carboxylic acid: - OH bonded to the C=O Ester: C-O bonded to the C=O Amide: C-N bonded to the C=O Acid chloride: Cl bonded to the C=O Carbonyl C has partial positive charge (  +) Carbonyl O has partial negative charge (  -).

13 13

14 Alkanes and Alkane Isomers Alkanes: Compounds with C-C single bonds and C-H bonds only (no functional groups) The formula for an alkane with no rings (acyclic) must be C n H 2n+2 where the number of C’s is n Alkanes are saturated with hydrogen (no more can be added) They are also called aliphatic compounds

15 15 A “saturated” fat (glyceryl stearate):

16 16 Alkane Isomers CH 4 = methane, C 2 H 6 = ethane, C 3 H 8 = propane The molecular formula of an alkane with more than three carbons can give more than one structure  C 4 (butane) = butane and isobutane  C 5 (pentane) = pentane, 2-methylbutane (isopentane), and 2,2-dimethylpropane (neopentane)

17 17 Methane, ethane, & propane

18 18 Butanes (C 4 H 10 ):

19 19 Pentanes (C 5 H 12 ):

20 20 Alkane Isomers

21 21 Alkane Isomers Alkanes with C’s connected to no more than 2 other C’s are straight-chain or normal alkanes Alkanes with one or more C’s connected to 3 or 4 C’s are branched-chain alkanes

22 22 Constitutional (Structural) Isomers Isomers that differ in how their atoms are arranged in chains are called constitutional (or structural) isomers Compounds other than alkanes can also be constitutional isomers of one another They must have the same molecular formula to be isomers

23 23 Constitutional Isomers

24 24 Condensed Structures of Alkanes We can represent an alkane in a brief form or in many types of extended form A condensed structure does not show bonds but lists atoms, such as  CH 3 CH 2 CH 3 (propane)  CH 3 (CH 2 ) 2 CH 3 (2,2-dimethylpropane)

25 25 Names of Small Hydrocarbons No. of CarbonsFormula Name(C n H 2n+2 ) 1MethaneCH 4 2EthaneC2H6C2H6 3PropaneC3H8C3H8 4ButaneC 4 H 10 5PentaneC 5 H 12 6HexaneC 6 H 14 7HeptaneC 7 H 16 8OctaneC 8 H 18 9NonaneC 9 H 20 10DecaneC 10 H 22

26 Alkyl Groups Alkyl group – remove one H from an alkane (a part of a structure) General abbreviation “R” (for Radical, an incomplete species or the “rest” of the molecule) Name: replace -ane ending of alkane with -yl ending  -CH 3 is “methyl” (from methane)  -CH 2 CH 3 is “ethyl” from ethane

27 Alkyl Groups

28 28 Alkyl Groups

29 29

30 30 Types of Alkyl groups a carbon at the end of a chain (primary alkyl group) a carbon in the middle of a chain (secondary alkyl group) a carbon with three carbons attached to it (tertiary alkyl group)

31 31 Types of Carbon Atoms

32 32 Types of Functional groups

33 33 Types of Hydrogens:

34 Naming Alkanes: IUPAC Compounds are given systematic names by a process that uses:

35 Naming Alkanes: IUPAC Follows specific rules  Named as longest contiunous chain of C’s  Carbons in that chain are numbered in sequence  Substituents are numbered at their point of attachment  Compound name is one word (German style)  Complex substituents are named similarly

36 36 1. Find the Parent: longest continuous carbon chain

37 37 2. Number the atoms in the chain with the end of the chain nearer the first substituent

38 38 3. Identify & number the substituents. When two substituents are present at an equal distance from either end of the longest chain, we number the ring beginning with the substituent first in the alphabet. In deciding on alphabetical oreder disregard multiplying prefixes such as “di” and “tri” etc. and the prefixes like sec- or tert. 3-Ethyl-5-methylheptane 3-Methyl-5-ethylheptane NOT

39 39 4. Wenn three or more substituents are present, we begin at the substituent that leads to the lowest set of locants.

40 40 4. Write the name

41 41 Practice problem 2.2: IUPAC name?

42 42 Solution:

43 43 Practice prob. 2.3: structure? 3-isopropyl-2-methylhexane C-C-C-C-C-C Two substituents: isopropyl & methyl Add hydrogens to complete the structure

44 44 Solution:

45 45 Problem 2.11: IUPAC names?

46 Naming Alkyl Halides Name is based on longest carbon chain  (Contains double or triple bond if present)  Number from end nearest any substituent (alkyl or halogen)  Halogens have same priority as alkyl groups

47 47

48 48 Naming with Multiple Halides If more than one of the same kind of halogen is present, use prefix di, tri, tetra If there are several different substituents (halogens or alkyls), number them and list them in alphabetical order

49 49 Naming if Two Halides or Alkyl Are Equally Distant from Ends of Chain Begin at the end nearer the substituent whose name comes first in the alphabet

50 Properties of Alkanes Called paraffins (low affinity compounds) because they are relatively unreactive They will burn in a flame, producing carbon dioxide, water, and heat CH O 2 → CO H 2 O + heat

51 Properties of Alkanes They react with Cl 2 in the presence of light to replace H’s with Cl’s (not easily controlled)

52 52 Physical Properties Boiling points and melting points increase as size of alkane increases Forces between molecules (temporary dipoles, dispersion) are weak

53 53 Physical Properties

54 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of  CH 2  units, (CH 2 )n, or C n H 2n Structure is shown as a regular polygon with the number of vertices equal to the number of C’s (a projection of the actual structure)

55 Cycloalkanes

56 56 Complex Cycloalkanes Naturally occurring materials contain cycloalkane structures Examples:  chrysanthemic acid (cyclopropane),  prostaglandins (cyclopentane),  steroids (cyclohexanes and cyclopentane)

57 57 Complex Cycloalkanes

58 58 Properties of Cycloalkanes Melting points are affected by the shapes and the way that crystals pack so they do not change uniformly

59 Naming Cycloalkanes Count the number of carbon atoms in the ring and the number in the largest substituent chain. If the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane. For an alkyl- or halo-substituted cycloalkane, start at a point of attachment as C1 and number the substituents on the ring so that the second substituent has as low a number as possible. When two substituents are present, we number the ring beginning with the substituent first in the alphabet. Wenn three or more substituents are present, we begin at the substituent that leads to the lowest set of locants Number the substituents and write the name

60 60 1. Find the parent: or butylcyclopropane

61 61 Number the substituents & write the name:

62 62 Examples:

63 63 Problem 2.15: IUPAC names?

64 Cis-Trans Isomerism in Cycloalkanes Rotation about C-C bonds in cycloalkanes is limited by the ring structure Rings have two “faces” and substituents are labeled as to their relative facial positions There are two different 1,2-dimethyl-cyclopropane isomers, one with the two methyls on the same side (cis) of the ring and one with the methyls on opposite sides (trans)

65 Cis-Trans Isomerism in Cycloalkanes

66 66 Stereoisomers Compounds with atoms connected in the same order but which differ in three-dimensional orientation, are stereoisomers The terms “cis” and “trans” should be used to specify stereoisomeric ring structures Recall that constitutional isomers have atoms connected in different order

67 67 Stereoisomers

68 68 Practice Prob. 2.4: Name?

69 69 Problem 2.18: IUPAC Name?

70 70 Gasoline: Octane Ratings

71 71 Chapter 2, Questions 30, 34, 35, 36, 37

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