Alkana. Dept Teknik Kimia FTUI

Transcription

1 Alkana C n 2n+2 Dept Teknik Kimia FTUI

2 ydrocarbons Aliphatic Aromatic

3 ydrocarbons Aliphatic Aromatic Alkana Alkena Alkuna

4 ydrocarbons Aliphatic Alkanes are hydrocarbons in which all of the bonds are single bonds. C C Alkana etana

5 ydrocarbons Aliphatic Alkenes are hydrocarbons that contain a carbon-carbon double bond. Alkena C C Etena

6 ydrocarbons Alkuna are hydrocarbons that contain a carboncarbon triple bond. Aliphatic C C Alkuna Asetilen

7 ydrocarbons The most common aromatic hydrocarbons are those that contain a benzene ring. Aromatic

8

9 Struktur alkana tetrahedral about carbon all bond angles are approximately 109.5

10 Penggambaran Alkana Ball-andstick model Line-angle formula Structural formula C 3 C 2 C 3 C 3 C 2 C 2 C 3 C 3 C 2 C 2 C 2 C 3 Propane Butane Pentane

11 Penamaan Alkana Suffix -ana specifies an alkanaana Prefix tells the number of carbon atoms Prefix methethpropbutpenthex- heptoctnondec- Carbons Prefix Carbons undec- 11 dodec- 12 tridec- 13 tetradec- 14 pentadec- 15 hexadec- 16 heptadec- 17 octadec- 18 nonadec- 19 eicos- 20

12 Penamaan Alkana Parent name: the longest carbon chain Substituent: a group bonded to the parent chain alkyl group: given the symbol R- Alkane Name Alkyl group Name C 4 Methane C 3 - Methyl group C 3 C 3 Ethane C 3 C 2 - Ethyl group

13 Penamaan Alkana Each substituent is given a name and a number C 3 C 3 CC Methylprop ane 2-metilpropana If there is one substituent, number the chain from the end that gives it the lower number C 3 C 3 C 2 C 2 CC Methylpen tane 2-metilpentana (not 4-meth ylp entane)

14 Penamaan Alkana If there are two or more identical substituents, number the chain from the end that gives the lower number to the substituent encountered first indicate the number of times the substituent appears by a prefix di-, tri-, tetra-, etc. use commas to separate position numbers ,4-Dimethylhexan 2,4-dimetilheksana e (n ot 3,5-d imethylhexan e) 5 6

15 Penamaan Alkana If there are two or more different substituents, list them in alphabetical order number from the end of the chain that gives the substituent encountered first the lower number Ethyl-5-methylh 3-etil-5-metilheptana eptane (not 3-methyl-5-ethylheptane)

16 Penamaan Alkana The prefixes di-, tri-, tetra-, etc. are not included in alphabetization alphabetize the names of substituents first and then insert these prefixes Ethyl-2,2-dimethylh 4-etil-2,2-dimetilheksana exane (not 2,2-dimethyl-4-eth ylh exane)

17 Physical Properties Boiling points: increase with increasing number of carbons decrease with chain brainching Alkanes are non-polar, soluble in nonpolar or slightly polar solvents, insoluble in water Intermolecular forces are van der Waals forces Less dense than water

18 Chemical Properties All alkanes burn in air to give CO2 and 2O alogenation Pyrolysis (cracking): decomposition of a compound by the action of heat alone

19 alogenation (mekanisme radikal bebas) Alkanes can react with halogens to form alkyl halides via free radical substitution pathways. A radical is

20 alogenation (mekanisme radikal bebas) Carbon radicals are formed by homolytic cleavage of covalent bonds using either: (1) Light ( h) (2) eat (Δ) (3) Radical Initiators (ROOR i.e. peroxides)

21 alogenation Stage I Initiation ( f ormation of the halogen radicals) The mechanism has three distinct stages. Stage II Propagation ( f ormation of product and another halogen radical) Stage III Termination ( multiple pathways to extinguish all radicals)

22 alogenation Initiation: The reaction begins with an initiation stage, which is the separation of the halogen (X 2 ) into two radicals (atoms with a single unpaired electron) by the addition of uv light.

23 alogenation Propogation: The initiation stage, or the formation of the chlorine radicals, is immediately followed by the propogation stages--stages directly involved in the formation of the product. In the last stage, the tertiary radical then reacts with another one of the chlorine molecules to form the product.

24 alogenation Termination: Side reactions that can stop the chain reaction are called termination stages.

25 alogenation excess halogen is used monohalogenation The most important steps of radical halogenation are those that lead to product formation the propagation steps

26 Radical Reactions Mechanism

27 Sources of Alkanes Natural gas 90-95% methane Petroleum gases (bp below 20 C) naphthas, including gasoline (bp C) kerosene (bp C) fuel oil (bp C) lubricating oils (bp above 350 C) asphalt (residue after distillation) Coal Biomass??????????

28 Cycloalkanes General formula C n 2n five- and six-membered rings are the most common Structure and nomenclature to name, prefix the name of the corresponding open-chain alkane with cyclo-, and name each substituent on the ring if only one substituent, no need to give it a number if two substituents, number from the substituent of lower alphabetical order if three or more substituents, number to give them the lowest set of numbers and then list substituents in alphabetical order

29 Cycloalkanes Line-angle drawings each line represents a C-C bond each vertex and line ending represents a C C C C C C C C C 2 C 2 C C 2 C2 C C C 3 C 3 C 8 1 6

30 Cycloalkanes Example: name these cycloalkanes (a) (b) (c) (d)

31 Bicycloalkanes Bicycloalkane: an alkane that contains two rings that share two carbons Bicyclo[4.4.0]decane (Decalin) Bicyclo[4.3.0]nonane (ydrindane) Bicyclo[2.2.1]heptane (Norbornane) (camphor) monoterpenes 1,7,7-trimethylbicyclo [2.2.1]heptan-2-one odorous components of plants

32 Bicycloalkanes Nomenclature parent is the alkane of the same number of carbons as are in the rings number from a bridgehead, along longest bridge back to the bridgehead, then along the next longest bridge, etc. show the lengths of bridges in brackets, from longest to shortest 1 one C bridgehead two C s 4 Bicyclo[2.2.1]h eptane

33 Isomers relationships among isomers

34 Cis,Trans Isomerism (Geometric isomers) Cis,trans isomers stereoisomers that are the result of the presence of either a ring or a carbon-carbon double bond

35 Cis,Trans Isomers 1,2-Dimethylcyclopentane C 3 C 3 3 C C 3 3 C C 3 cis-1,2-d imeth ylcyclop entane 3 C C 3 trans-1,2-d imethylcyclop entane

36 Cis,Trans Isomerism 1,4-Dimethylcyclohexane C 3 3 C 3 C C 3 C 3 C 3 3 C t rans-1,4-d imethylcyclohexane 3 C cis-1,4-d imethylcycloh exane

37 Cis,Trans Isomerism trans-1,4-dimethylcyclohexane the diequatorial-methyl chair conformation is more stable by approximately 2 x (7.28) = kj/mol C 3 (less stable) C 3 3 C (more stable) C 3

38 Cis,Trans Isomerism cis-1,4-dimethylcyclohexane C 3 3 C C 3 conformation s are of equal s tability C 3

39 Cis,Trans Isomerism The decalins A B trans-decalin A B cis-decalin

40 Conformations Conformation: any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond Newman projection: Newman projection: a way to view a molecule by looking along a carbon-carbon single bond

41 Conformations Staggered conformation: a conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as far apart as possible from the atoms or groups on an adjacent carbon

42 Conformations Eclipsed conformation: a conformation about a carbon-carbon single bond in which the atoms or groups of atoms on one carbon are as close as possible to the atoms or groups of atoms on an adjacent carbon

43 Conformations Torsional strain also called eclipsed interaction strain strain that arises when nonbonded atoms separated by three bonds are forced from a staggered conformation to an eclipsed conformation the torsional strain between eclipsed and staggered ethane is approximately 12.6 kj (3.0 kcal)/mol kj/mol

44 Conformations Dihedral angle (Q) Dihedral angle (Q): the angle created by two intersecting planes

45 Conformations Ethane as a function of dihedral angle

46 Conformations conformations of butane as a function of dihedral angle

47 Anti Butane Energy-minimized anti conformation the C-C-C bond angle is and all -C- bond angles are between and 107.9

48 Eclipsed Butane

49 Cyclopropane angle strain: the C-C-C bond angles are compressed from to 60 torsional strain: there are 6 sets of eclipsed hydrogen interactions strain energy is about 116 kj (27.7 kcal)/mol

50 Cyclobutane puckering from planar cyclobutane reduces torsional strain but increases angle strain the conformation of minimum energy is a puckered butterfly conformation strain energy is about 110 kj (26.3 kcal)/mol

51 Cyclopentane puckering from planar cyclopentane reduces torsional strain, but increases angle stain the conformation of minimum energy is a puckered envelope conformation strain energy is about 42 kj (6.5 kcal)/mol

52 Cyclohexane Chair conformation: the most stable puckered conformation of a cyclohexane ring all bond C-C-C bond angles are all bonds on adjacent carbons are staggered

53 Cyclohexane In a chair conformation, six are equatorial and six are axial

54 Cyclohexane For cyclohexane, there are two equivalent chair conformations all C- bonds equatorial in one chair are axial in the alternative chair, and vice versa

55 Cyclohexane Boat conformation: a puckered conformation of a cyclohexane ring in which carbons 1 and 4 are bent toward each other there are four sets of eclipsed C- interactions and one flagpole interaction a boat conformation is less stable than a chair conformation by 27 kj (6.5 kcal)/mol

56 Cyclohexane Twist-boat conformation approximately 41.8 kj (5.5 kcal)/mol less stable than a chair conformation approximately 6.3 kj (1.5 kcal)/mol more stable than a boat conformation

57 Cyclohexane

58 Methylcyclohexane Equatorial and axial methyl conformations kj/mol C 3 C 3