Organic Chemistry. February 18, 2014

Transcription

1 Organic Chemistry February 18, 2014

2 What does organic mean? Organic Describes products Grown through natural biological process Without synthetic materials In the 18 th century Produced by a living system Could not be produced in a lab

3 Organic In 1828 German chemist: Friedrich Wohler Reacted two inorganic compounds Obtained urea (organic compound) Our Definition Organic Compound A molecular compound containing carbon Not including (CO (g), CO2 (g), CN (g) )

4 Organic Chemistry Organic Chemistry Is the study of compounds in which carbon is the principle element Example: animals, fossil fuels, plants

5 Carbon Atom can form four bonds Four valence electrons Bond angle: o Atoms can bond together to form Chains, Rings, Spheres, Sheets, Tubes Form combinations of bonds Single, Double, and Triple bonds Carbon chains are the backbone of many molecules

6 ydrocarbons A compound containing only carbon and hydrogen atoms There are two main classes: aliphatic and aromatic

7 ydrocarbons Aliphatic hydrocarbons A compound that has chains or rings of carbon Does not include aromatics Aromatic hydrocarbons Compound based on a ring of six carbons Formula: C 6 6 All six bonds: intermediate between single and double bonds

8 Alkanes Saturated hydrocarbon Only has single bonds between carbons General Formula C n 2n+2

9 First 10 Alkanes C 4 C 2 6 C 3 8 C 4 10 C 5 12 C 6 14 C 7 16 C 8 18 C 9 20 C methane ethane propane butane pentane hexane heptane octane nonane decane Prefix: based on the number of carbons in the longest chain Suffix: ane ending

10 Diagrams Expanded Structural Diagrams The normal structures of a few alkanes methane propane hexane C C C C C C C C C C

11 Building/Drawing Alkanes C 2 6 C 3 8 C 5 12

12 Structural Isomers Structural Isomers Compounds with the same chemical formula ave the same molecular mass Different arrangements of atoms Physical and Chemical properties may be different C C C C C C C C C C

13 Alkyl Groups One (or more) carbon branches attached to the main chain of the hydrocarbon Naming Drop the ane of the corresponding alkane End with yl General Formula: C n 2n-1 Type of substituent group Anything that replaces hydrogen in an organic molecule

14 Alkyl Group Carbon chain added to the parent chain methyl ethyl propyl butyl pentyl hexyl Follow the same prefixes as the parent chain End in yl

15 Naming Alkanes 1. Identify the longest continuous carbon chain BE CAREFUL! It may not be in a straight line 2 C C 2 C C 3 C 3 C 3 Longest chain is 5 carbon atoms 2. Number the carbon atoms Start with the end nearest to the substituent group C C 2 C C C 3 C 3

16 Naming Alkanes 3. Name the chain by adding -ane pentane C C 2 C C 3 4. Name the substituent group Methyl 5 C 3 C 3 5. Attach the name of the group as a prefix AND the attached carbon number 2-methylpentane

17 Naming Alkanes 6. If two or more of the same group occur Use prefixes: di, tri, tetra, etc. Locate their position on the main chain Separate numbers by commas Separate words by hyphens C C 2 C C C 3 C 3 C 3 2,3-dimethylpentane

18 Naming Alkanes 7. If different groups are present Arrange in alphabetical order Use numbers to indicate their position C 3 C C C C C 2 C C C 2 C 3 C 3 C 2 C ethyl - 2,3,6 - trimethyloctane

19 Alkyl alides An alkane in which one or more hydrogen atoms have been replaced by one or more halogen atoms F- fluoro Cl- chloro Br- bromo I- iodo Other common groups NO 2 - nitro N 2 - amino

20 Naming Alkyl alides Use the same rules as naming alkanes with branches 1-bromo-3,4-dimethylpentane C 3 C 3 2 C C 2 C C Br C 3 1,1,2-trichloro-3-methylpentane Cl 2 C C 3 C C C C 3 Cl Cl C 3 F C 2 4-ethyl-2-fluoroheptane C 3 C C 2 C C 2 C 2 C 3

21 Drawing Organic Molecules Expanded Structural Diagrams Shows all bonds between atoms Condensed Structural Diagrams Combine carbon atoms and the hydrogens bonded C C C C C C 3 C 2 C 2 C 2 C 3 Line Diagrams Only show carbon bonds Assumed hydrogens are attached appropriately

22 Alkenes Contain at least one carbon double bond (C=C) Unsaturated Less than the maximum quantity of hydrogen More reactive than alkanes General Formula: C n 2n

23 Examples Ethene C 2 4 C C Propene C 3 6 Butene C 4 8 C C C 3 C C C C C 2 C 3 C 3 C 3 1-butene 2-butene but-1-ene but-2-ene

24 Naming Alkenes General Rules for Naming 1. All alkane rules apply 2. Change the ending to -ene Must include double bond(s) in the chain 3. Start numbering carbons closest to double bond

25 Naming Alkenes 4. Include the number of the bonded carbon Either in front of chain name or before suffix 5. More than one double bond Use prefix before suffix di, tri, tetra, etc. 1, 3 pentdiene pent-1,3-diene

26 Geometric Isomers Carbon-carbon double bonds Not free to rotate (sigma + pi bonds) Two structures can exist Example: 2-butene C C C C C 3 C 3 C 3 C 3 cis-2-butene trans-2-butene

27 Geometric Isomers cis Latin for on this side C or sis trans Latin across trans atlantic Cl C C Cl cis-1,2-dichloroethene (mp = -81 O C; bp = 60 O C) Cl C C Cl trans-1,2-dichloroethene (mp = -81 O C; bp = 48 O C)

28 Alkynes Contain at least one carbon triple bond Unsaturated Less than the maximum quantity of hydrogen More reactive than alkanes (and alkenes) General Formula: C n 2n-2

29 Naming Alkynes General Rules for Naming 1. All alkane/alkene rules apply 2. Change the ending to -yne Must include triple bond(s) in the chain 3. Start numbering carbons closest to triple bond

30 Naming Alkynes 4. Include the number of the bonded carbon Either in front of chain name or before suffix 5. More than one triple bond Use prefix before suffix di, tri, tetra, etc. C 3 C C C 3 C 2 C 2 C C Cl 2-butyne but-2-yne 4-chloro-1-butyne 4-chlorobut-1-yne

31 Cyclic Aliphatics Carbon atoms can also be arranged in rings Named after the corresponding open chain Same rules apply for alkanes, alkenes, alkynes Prefix cyclo Substituents can be named after based on position 2 C C 2 2 C C 2 C C C 2 C 2 C 2 cyclobutane cyclopentene 3-ethylcyclopentene C C C 2 C 2 C C 2 C 3

32 Cyclic Aliphatics For convenience, you can draw the corresponding polygon for each size of carbon ring Triangle (3 carbon), square (4 carbon), etc. It is understood that the appropriate number of hydrogens are attached C 3 C 3 C 3 cyclopentene 1,2,3-trimethylcyclohexane

33 Structural Isomers The number of structural isomers increase as the number of carbon atoms increase

34 Properties of ydrocarbons

35 Physical Properties of ydrocarbons Since C and have similar electronegativities, there are covalent bonds Generally non-polar molecules The main intermolecular force is van der Waals forces. These are weak, making the compound easy to separate. Van der Waals forces: the attraction of electrons of one molecule for the the nuclei of another molecule As the compound gets larger in size, the strength of VDW forces increases, leading to higher MP and BP

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37 Fractional Distillation

38 Reactions of ydrocarbons

39 Reactions of Alkanes ALL hydrocarbons undergo COMBUSTION REACTIONS, making them useful fuels Complete Combustion: chemical reaction that involves a compound reacting with O 2 to produce carbon dioxide, water and thermal energy

40 Reactions of Alkanes Alkanes are generally unreactive Single C-C bonds are hard to break Primarily undergo SUBSTITUTION REACTIONS Reaction that replaces a hydrogen atom with another atom or group of atoms

41 Reactions of Alkanes can be substituted by a halogen atom alides (Br 2 ) or ydrogen halides (Br) Form ALKYL ALIDES Usually requires heat or UV light Reactions involving F 2 are vigorous

42 Reactions of Alkanes As the reaction proceeds: Additional bromines can be added resulting in a mixture of brominated products Separated by fractional distillation

43 Reactions of Alkenes and Alkynes Due to the presence of multiple bonds Alkenes/Alkynes are MORE REACTIVE than alkanes For example, reactions with Br 2 are vigorous at room temperature Alkanes require heat or UV light to react Undergo ADDITION REACTIONS Atoms are added to the compound without loss of hydrogen

44 Reactions of Alkenes and Alkynes There are FOUR types of ADDITION reactions Classified by the type of compound being reacted 1. alogenation reaction with halogen

45 Reactions of Alkenes and Alkynes 2. ydrogenation reaction with 2

46 Reactions of Alkenes and Alkynes 3. ydrohalogenation reaction with hydrogen halides (X)

47 Reactions of Alkenes and Alkynes 4. ydration reaction with water

48 Markovnikov s Rule When a hydrogen halide or water molecule reacts with an Alkene, the hydrogen atom will generally bond to the carbon atom in the multiple bond that has the most hydrogen atoms already bonded to it

49 Aromatic ydrocarbons Aromatic hydrocarbons are benzene or a compound that contains a benzene ring Benzene has the formula: C 6 6 C 1 C 2 C 6 C 3 C 5 C 4

50 Aromatic ydrocarbons Electrons involved in the double bonds are equally shared among the 6 carbons Benzene can be thought of as a hybrid of two resonance forms A common way to represent benzene

51 Aromatic ydrocarbons General Rules for Naming The benzene ring is usually considered the parent chain 1. If an alkyl group is attached to benzene, the compound is named alkylbenzene F Cl Br NO 2 fluorobenzene bromobenzene chlorobenzene nitrobenzene

52 Aromatic ydrocarbons 2. If more than one alkyl group is attached to the benzene ring, number each using the lowest combination of numbers (IUPAC) 6 Cl Cl 1,2-dichlorobenzene Cl Cl 1,3-dichlorobenzene 2 3

53 Aromatic ydrocarbons Occasionally, benzene groups are found as a substituent to more complex hydrocarbon chains. The benzene is called phenyl C 3 C 3 3-chloro-2-methyl-4-phenyl-2-pentene C C C C 3 Cl

54 Ortho, Meta, Para Alternate system using relative position Example: diethylbenzene o-diethylbenzene m-diethylbenzene p-diethylbenzene o = ortho m = meta p = para

55 Practice

56 Properties of Aromatics Most are liquids at room temperature Some are crystalline solids Symmetrical structures Non-polar (unless it has an electronegative substituent) Generally insoluble in water

57 Reactions of Aromatic Compounds Unique bonding makes the bond strength greater than alkenes Much less reactive than alkenes Undergoes SUBSTITUTION Reactions Like alkanes

58 Reactions of Aromatic Compounds Further reactions with halogens (Br 2 ) can result in additional substitutions. In theory, the bromine can replace any hydrogen.

59 Substitution Reactions with Benzene

60 Difference with 6 carbon rings