Chapter 10 Introduction to Organic Chemistry: Alkanes

Transcription

1 hapter 10 Introduction to Organic hemistry: Alkanes 1

2 Organic hemistry An organic compound is a compound made from carbon atoms has one or more atoms has many atoms may also contain O, S, N, and halogens usually has carbon written first 2

3 Organic ompounds Typical organic compounds have covalent bonds have low melting points have low boiling points are flammable are soluble in nonpolar solvents are not soluble in water Vegetable oil is an organic compound and not soluble in water. 3

4 4 omparing Organic and Inorganic ompounds

5 Bonding in Organic ompounds In organic compounds, carbon has 4 valence electrons and hydrogen has carbon achieves an octet by forming four bonds, with each line representing 2 electrons 4, methane 5

6 Tetrahedral Structure of arbon 4 VSEPR theory predicts that a carbon atom with four single, covalent bonds has a tetrahedral shape. Methane is represented using different models: (a) tetrahedron, (b) ball-andstick model, (c) space-filling model, (d) expanded structural formula. 6

7 Tetrahedral Structure of arbon 2 6 In ethane, each carbon forms covalent bonds to another carbon and three hydrogen atoms each carbon atom retains its tetrahedral shape Ethane, 3 3 7

8 Tetrahedral Structure of arbon 2 6 In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape. Representations of ethane: (a) tetrahedral shape of each carbon, (b) ball-and-stick model, (c) space-filling model, (d) expanded structural formula. 8

9 Learning heck In the butane molecule, 4 10, predict the shape around each carbon atom. 9

10 Solution In the butane molecule, 4 10, predict the shape around each carbon atom. Each carbon atom has four single covalent bonds and therefore a tetrahedral shape. 10

11 Alkanes Alkanes are organic molecules containing primarily single bonds commonly used as fuels for heaters and cooktops whose names end in ane named by using the number of carbon atoms connected in a continuous chain 11

12 12 IUPA Naming of the First Ten Alkanes

13 ondensed Structural Formulas In a condensed structural formula, each carbon atom and its attached hydrogen atoms are written as a group a subscript indicates the number of hydrogen atoms bonded to each carbon atom of butane, four carbon atoms are attached in a straight line butane 13

14 ondensed Structural Formulas Alkanes are written with structural formulas that are expanded to show each bond condensed to show each carbon atom and its attached hydrogen atoms Expanded ondensed Expanded ondensed = 3 = 2 14

15 Writing Structural Formulas arbon atoms in a chain maintain tetrahedral shape are connected in a zigzag pattern are drawn as two-dimensional can be written in several conformations 15

16 Expanded, ondensed, and Skeletal Structures A hexane molecule can be represented in several ways: a molecular formula a ball-and-stick model an expanded structural formula a condensed structural formula a skeletal formula 16

17 Learning heck Write the condensed structural formula for A. ethane B. heptane 17

18 Solution Write the condensed structural formula for A. ethane 3 3 B. heptane

19 ycloalkanes ycloalkanes are cyclic alkanes have two less hydrogen atoms than the open chain are named by using the prefix cyclo before the name of the alkane chain with the same number of carbon atoms propane, 3 8 cyclopropane, n (2n+2) n 2n

20 20 Formulas of ycloalkanes

21 Learning heck Name the following alkanes: A B D. 21

22 Solution Name the following alkanes: A butane B. cyclopropane octane D. cyclohexane 22

23 Substitutions - Isomers Isomers have the same molecular formula with different atom arrangements of butane ( 4 10 ) are a straight chain and a branched chain The isomers of butane have the same number and type of atoms, but the atoms are bonded in a different order. 23

24 Substituents and Alkyl Groups Substituents are atoms or groups of atoms attached to the carbon chain and include alkyl and halo groups. Alkyl groups are carbon branches attached to carbon chains named with a yl ending alo substituents are halogens attached to the carbon chain named as fluoro, chloro, bromo, or iodo 24

25 25 Substituents and Alkyl Groups

26 Guide to Naming Alkanes with Substituents 26

27 Write IUPA Names for Alkanes with Substituents Give the IUPA name for the following compound: l 3 Step 1 Write the alkane name of the longest chain of carbon atoms. The longest chain has five carbons, pentane. l 3 27

28 Write IUPA Names for Alkanes with Substituents Step 2 Number the carbon atoms starting from the end nearer a substituent. l Step 3 Give the location and name of each substituent (in alphabetical order) as a prefix to the name of the main chain. 2-chloro-3-methylpentane 3 28

29 Learning heck Give the IUPA name for the following compound: Br 3 Br 29

30 Solution Give the IUPA name for the following compound: Br 3 Br Step 1 Write the alkane name of the longest chain of carbon atoms. The longest chain has four carbons, butane. Br 3 Br 30

31 Solution Step 2 Number the carbon atoms starting from the end nearer a substituent. Br Br Step 3 Give the location and name of each substituent (in alphabetical order) as a prefix to the name of the main chain. 1,2-dibromo-3-methylbutane 31

32 Naming ycloalkanes with Substituents Give the IUPA name for the following cycloalkane. 2 3 Step 1 Write the alkane name of the longest chain of carbon atoms. The longest chain is a six-member ring, cyclohexane

33 Solution Step 2 Number the carbon atoms starting from the end nearer a substituent. Step 3 Give the location and name of each substituent (in alphabetical order) as a prefix to the name of the main chain. For cycloalkanes with just one substituent, there is no need to give the location of the substituent: ethylcyclohexane

34 Drawing Formulas for Alkanes Draw the structure for 1-chloro-1,2-dimethylheptane heptane 7-carbon chain methyl group on carbon 1 and 2 chlorine on carbon 1 34

35 35 Guide to Drawing Formulas for Alkanes

36 Learning heck Draw the condensed structural formula for 3-bromo-1-chlorobutane. 36

37 Solution Draw the condensed structural formula for 3-bromo-1-chlorobutane. Step 1 Draw the main chain of carbon atoms. The longest chain in butane has four carbon atoms. Step 2 Number chain and place the substituents on the carbons indicated by the numbers bromo: Br goes on carbon 3. 1-chloro: l goes on carbon 1. l Br l Br 37

38 Solution Draw the condensed structural formula for 3-bromo-1-chlorobutane. Step 3 Add hydrogen to complete four bonds to each carbon l Br l Br 3-bromo-1-chlorobutane 38

39 Learning heck Name each of the following cycloalkanes. A. 3 2 B. 3. l 39

40 Solution Name each of the following cycloalkanes. 3 A. methylcyclopropane 2 3 B. ethylcyclobutane l. chlorocyclopentane 40

41 Some Uses of Alkanes Alkanes with one to four carbons are gases at room temperature and are widely used as heating fuels. methane, ethane, propane, butane Butane has four carbons: Alkanes with five to eight carbons are highly volatile liquids at room temperature, making them useful in fuels such as gasoline. pentane, hexane, heptane, octane Octane has eight carbons: Alkanes with 9 17 carbons are liquids with higher boiling points and are found in motor oils, mineral oil, kerosene, diesel, and jet fuels. Decane has 10 carbons: Alkanes with 18 or more carbons have high molar masses are waxy solids at room temperature are used in waxy coatings of fruits and vegetables 41

42 Solubility and Density of Alkanes Alkanes are nonpolar insoluble in water less dense than water flammable in air The crude oil in oil spills floats on top of the water, forming a thin layer on the surface because it is less dense than water. 42

43 ombustion of Alkanes Alkanes have strong bonds react with oxygen gas to make carbon dioxide and water in combustion reactions release energy when bonds are broken in combustion reactions 4 (g) + 2O 2 (g) O 2 (g) O(g) + energy 43

44 Learning heck Propane is a fuel often used in barbeques. Write a balanced equation for the complete combustion of propane. 44

45 Solution Unbalanced equation: O 2 Balance : O 2 Balance : O 2 Balance O: O 2 O O 3O O 3O O 3O O (balanced) 45

46 Elements in Organic ompounds In organic molecules, carbon atoms bond with four bonds mostly with and other atoms sometimes to O, N, S sometimes to halogens F, l, and Br 46

47 Functional Groups Functional groups are a characteristic feature of organic molecules that behave in a predictable way composed of an atom or group of atoms groups that replace a hydrogen atom in the corresponding alkane a way to classify families of organic compounds 47

48 Alkenes, Alkynes, and Aromatic ompounds Alkenes contain a double bond between adjacent carbon atoms. Alkynes contain a triple bond. Aromatic compounds contain a ring of six carbon atoms called benzene. 48

49 49 omparing Alkenes, Alkynes, and Aromatic ompounds

50 Learning heck Identify the following compounds as an alkene, alkyne, or aromatic compound. A. B.. 50

51 Solution Identify the following compounds as an alkene, alkyne or aromatic compound. A. aromatic B. alkene. alkyne 51

52 Alcohols, Thiols, and Ethers An alcohol contains the hydroxyl ( O) functional group. A thiol contains the thiol ( S) functional group. An ether contains an oxygen atom bonded to two carbon atoms ( O ) functional group. 52

53 Aldehydes and Ketones An aldehyde contains a carbonyl group (=O), which is a carbon atom with a double bond to an oxygen atom. The carbonyl carbon is attached to a hydrogen. In a ketone, the carbon of the carbonyl group (=O) is attached to two carbon atoms. O O 53

54 arboxylic Acids and Esters arboxylic acids contain the carboxyl group, which is a carbonyl group attached O to a hydroxyl group. OO An ester contains the carboxyl group between carbon atoms. OO 3 O O O 54

55 Amines Amines have a functional group that contains a nitrogen atom are derivatives of ammonia, N 3, in which one, two, or three hydrogen atoms are replaced with carbons N 3 N 3 N 3 55

56 Amides Amides have an amine group instead of an O group on the carbonyl carbon O N are an important biological functional group, the simplest amide being urea 2 N O N 2 56

57 lassification of Organic ompounds 57

58 Learning heck lassify each of the following as an alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, or amide. A. B.. D. E. 58

59 Solution lassify each of the following as an alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, or amide. A. B.. alcohol ether amine D. E. carboxylic acid ester 59

60 oncept Map Organic ompounds 60