Chapter 3 An Introduction to Organic Compounds, Nomenclature, Physical Properties, and Representation of Structure 1 Dr. Sujatha Krishnaswamy Chemistry Faculty Chandler Gilbert Community College

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Alkanes and Cycloalkanes Acyclic alkanes contain only linear and branched chains of carbon atoms. They are also called saturated hydrocarbons because they have the maximum number of hydrogen atoms per carbon. Cycloalkanes contain carbons joined in one or more rings. 3

4 Petroleum is a complex mixture of alkanes and cycloalkanes that can be separated by distillation.

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Butane and isobutane are isomers - two different compounds with the same molecular formula. Specifically, they are constitutional or structural isomers. Constitutional isomers differ in the way the atoms are connected to each other.

Straight Chain Alkanes 7

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9 Naming Branched Alkanes 1. For a branched-chain hydrocarbon, the alkane corresponding to the longest chain is taken as the parent chain and its name is the root name

10 Alkyl Substituents

11 2. If there are two possible chains with the same number of carbons, use the chain with the greater # of substituents.

12 3. Number from the end of the chain that gives the first substituent encountered the lower number.

13 4. If two substituents are equidistant, look for the next closest group.

14 5. If the same substituent occurs more than once, the number of each carbon of the parent chain on which it occurs is given and the number of times it occurs is shown by di-, tri-, tetra-, etc.

15 6. If there are two or more different substituents, list them in alphabetical order, and number from the end of the chain that gives the substituent encountered first the lower number

16 7. The prefixes di-, tri-, tetra- etc. are not included in alphabetization. 8. Neither are hyphenated prefixes such as sec- and tert-.. The prefix iso- is not hyphenated, and is included in alphabetization.

Name this alkane. 17

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Name these alkanes. 20

Types of Carbon Atoms 21

Types of Hydrogen Atoms 22

Identify the various carbon as 1 0, 2 0 or

24 Cycloalkanes

Some Interesting cycloalkanes 25 Fig. 4.4

Cycloalkanes in Drugs 26

Nomenclature of Cycloalkanes 27 Find the parent cycloalkane.

For rings with more than one substituent 28

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Note the special case of an alkane composed of both a ring and a long chain. If the number of carbons in the ring is greater than or equal to the number of carbons in the longest chain, the compound is named as a cycloalkane. 30

Name these cycloalkanes. 31

Name these cycloalkanes. 32

Stereoisomers 33

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Are these cis or trans isomers? 35

Conformations of Alkanes 36

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End-on representations for conformations are commonly drawn using a convention called a Newman projection. HOW TO Draw a Newman Projection Step [1] Look directly down the C-C bond (end-on), and draw a circle with a dot in the center to represent the carbons of the C-C bond. HOW TO Draw a Newman Projection 38

Step 2. Draw in the bonds. Draw the bonds on the front C as three lines meeting at the center of the circle. Draw the bonds on the back C as three lines coming out of the edge of the circle. Step 3. Add the atoms on each bond. 39

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A staggered conformation with two larger groups 180° from each other is called anti. A staggered conformation with two larger groups 60° from each other is called gauche. The staggered conformations are lower in energy than the eclipsed conformations. Anti and Gauche Conformations 41

Steric strain is an increase in energy resulting when atoms are forced too close to one another. Gauche conformations are generally higher in energy than anti conformations because of steric strain. Steric Strain 42 Page # 82 Problem 38

In reality, cyclohexane adopts a puckered “chair” conformation, which is more stable than any other possible conformation. Cyclohexane 43

44 The chair conformation of cyclohexane

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46 Ring Flip Animation

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48 The following cyclohexane has three substituents – red, yellow and blue – undergoes a ring flip to its alternate chair conformation. Identify each substituent as axial or equatorial in the ring flipped form.

Methyl Cyclohexane 49

Disubstituted Cyclohexanes 50

51 Problem 32

52 1. Page 84 Problem 63 Draw the most stable conformation of 1,2,3,4,5,6-hexachlorocyclohexane. 2. Page 83 Problem 55 d, e, f 3. Page 84 Problem 58

Importance of Functional Groups Functional groups distinguish one organic molecule from another. A functional group determines all of the following properties of a molecule: bonding and shape type and strength of intermolecular forces physical properties nomenclature chemical reactivity 53

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A molecule can contain many functional groups. 57

Identify the functional groups in 58

Identify the functional groups in 59

60 Paclitaxel (TAXOL, isolated from the Pacific yew tree, Taxus brevifolia), is clinically useful in the treatment of ovarian cancer. Identify the functional groups in TAXOL.