Alkenes and Alkynes Notes PDF

Alkenes and Alkynes  HYDROCARBONS Large family of organic compounds Composed of only carbon and hydrogen Saturated Unsaturated hydrocarbons hydrocarbons Alkanes Alkenes, Alkynes & C-C...

Alkenes and Alkynes  HYDROCARBONS Large family of organic compounds Composed of only carbon and hydrogen Saturated Unsaturated hydrocarbons hydrocarbons Alkanes Alkenes, Alkynes & C-C Aromatic C=C C≡C  Alkenes and Alkynes Unsaturated compounds: ❑ Have fewer hydrogen atoms attached to the carbon chain than ❑ alkynes with alkanes. triple C≡C bonds ❑ alkenes with double C=C bonds Containing triple bonds are alkynes. ❑ Containing double bond are alkenes. CnH2n-2 CnH2n  ALKENES AND ALKYNES Alkene and alkyne are called olefin ⚫ Olefins are examples of unsaturated hydrocarbons (compounds that contain only hydrogen and carbon and at least one double or triple bond). BOND ANGLES IN ALKENES According to Valence-Shell Electron-Pair Repulsion Theory (VSEPR): Three groups in a double bond are bonded at 120° angles. Alkenes are flat because the atoms in a double bond lie in the same plane. BOND ANGLES IN ALKYNES NAMES FOR ALKANES, ALKENES, AND ALKYNES  NAMING ALKENES The names of alkenes use the corresponding alkane name change the ending from -ane to -ene Alkene IUPAC Common H2C=CH2 Ethene Ethylene H2C=CH─CH3 Propene Propylene Cyclohexene  NAMING ALKYNES The names of alkynes use the corresponding alkane name change the ending from -ane to -yne Alkyne IUPAC Common HC≡CH Ethyne Acetylene HC≡C─CH3 Propyne COMMON NAMES OF SOME ALKENES  NAMING OF ALKENES Write the IUPAC name for CH2═CH─CH2─CH3 STEP 1 Name the longest carbon chain with a double ; butene STEP 2 Number the chain from the end nearer the double CH2═CH─CH2─CH3 1 2 3 4 STEP 3 Give the location and name of the double bond. old system: 1-butene new system: but-1-ene  NAMING OF ALKYNES Write the IUPAC name for CH3─CH≡CH─CH3. STEP 1 Name the longest carbon chain with a triple bond: butyne STEP 2 Number the chain from the end nearer the triple bond: CH3─CH≡CH─CH3 1 2 3 4 STEP 3 Give the location and name of the triple bond. old system: 2-butyne new system: but-2-yne  NAMING ALKENES WITH SUBSTITUENTS Write the IUPAC name for CH3 │ CH3─CH─CH=CH─CH3 STEP 1 Name the longest carbon chain: pentene STEP 2 Number the chain from the end nearer the double or triple bond: CH3 │ CH3─CH─CH=CH─CH3 5 4 3 2 1 STEP 3 Give the location and name of the substituent and double or triple bond: old system: 4-methyl-2-pentene new system : 4-methylpent-2-ene  Dienes, Trienes Alkenes that contain more than one double bond. Alkene name: -ne diene, triene, … 2 4 1 2 3 1 1 2 3 NAMING ALKENES  NAMING ALKYNES WITH SUBSTITUENTS CH3 │ Write the IUPAC name for HC≡C─CH─CH3. STEP 1 Name the longest carbon chain: butyne STEP 2 Number the chain from the triple bond: CH3 │ HC≡C─CH─CH3 1 2 3 4 STEP 3 Give the location and name of the substituent and double or triple bond: old system: 3-Methyl-1-butyne new system : 3-Methylbut-1-yne NAMING ALKYNES WITH SUBSTITUENTS NAMING ALKYNES WITH SUBSTITUENTS ⚫ A) 2,5-Dimethyl-3-hexyne ⚫ B) 3,3-Dimethyl-1-butyne  NAMING ALKYNES WITH SUBSTITUENTS compounds containing both double and triple bond are called enynes. starts numbering near to the multiple bond whether double or triple. if the distance is the same double bonds receive lower numbers than triple bond. NAMING ALKYNES WITH SUBSTITUENTS  SEATWORK Give the IUPAC name for each of the following: 1) CH2═CH─CH2─CH3 2) CH3─CH═CH─CH3 CH3 | 3) CH3─CH═C─CH3 CH3 | 4) CH3─C≡C─CH─CH3  SEATWORK Give the IUPAC name for each of the following: 1) CH2═CH─CH2─CH3 1-butene or but-1-ene 2) CH3─CH═CH─CH3 2-butene or but-2-ene CH3 | 3) CH3─CH═C─CH3 2-methyl-2-butene 2-methylbut-2-ene CH3 | 4) CH3─C≡C─CH─CH3 4-methyl-2-pentyne 4-methylpent-2-yne  NAMING OF CYCLOALKYNES Cyclopropyne cyclooctyne  NAMING OF CYCLOALKYNES Number the carbon atoms of the ring double bond 1 and 2 in the direction that gives the substituent lower number. No. location List substituents in for C=C alphabetical order.  NAMING OF CYCLOALKYNES Rings have cyclo as prefix  EXAMPLE ⚫ a) 1,2-Dimethylcyclohexene ⚫ b) 4,4-Dimethylcycloheptene  Physical Properties alkynes ❑Alkynes have low melting points and boiling points. ❑Melting point and boiling point increase as the number of carbons increases. ❑Alkynes are soluble in organic solvents and insoluble in water.  PHYSICAL PROPERTIES ALKENE non-polar or weakly polar no hydrogen bonding relatively low mp/bp ~ alkanes water insoluble Importance: common group in biological molecules starting material for synthesis of many plastics  POLYMERS Polymers are large, long-chain molecules found in nature, including cellulose in plants, starches in food, and proteins and DNA in the body also made synthetically, such as polyethylene and polystyrene, Teflon, and nylon made up of small repeating units called monomers made by reaction of small alkenes  POLYMERIZATION In polymerization, small repeating units called monomers join to form a long chain polymer. COMMON SYNTHETIC POLYMERS ALKENES AND THEIR POLYMERS MORE MONOMERS AND POLYMERS  ETHENE (ETHYLENE) Ethene, or ethylene, is the alkene C2H4 has two carbon atoms connected by a double bond has two H atoms bonded to each C atom is flat with all the C and H atoms in the same plane is used to accelerate the ripening of fruits  CIS AND TRANS ISOMERS In an alkene, cis and trans isomers are possible because the double bond is rigid cannot rotate has groups attached to the carbons of the double bond that are fixed relative to each other  NAMING CIS–TRANS ISOMERS The prefixes cis- or trans- are placed in front of the alkene name when there are cis–trans isomers. cis- trans- cis-1,2-Dibromoethene trans-1,2-Dibromoethene  CIS–TRANS ISOMERISM Cis–trans isomers do not occur if a carbon atom in the double bond is attached to identical groups. (not cis or trans) (not cis or trans)  PHEROMONES A pheromone is a chemical messenger emitted by insects in tiny quantities called bombykol is emitted by the silkworm moth to attract other moths and has one cis and one trans double bond CIS–TRANS ISOMERS EXAMPLE cis-1,2-Dibromoethene trans-2-Butene 1,1-Dichloropropene EXAMPLES  EXAMPLES CIS-1-chloro-2-butene TRANS-1-chloro-2-butene.  AROMATIC COMPOUNDS Aromatic was used to described some fragrant compounds in early 19th century unsaturated hydrocarbon Benzene from coal distillate  AROMATIC COMPOUNDS benzaldehyde from peaches, cherries and almonds  AROMATIC COMPOUNDS Toluene tolu balsam a fragrant brown balsam obtained from a South American tree, used in perfumery and medicine. common names toluene = methylbenzene  NAMES OF AROMATIC HYDROCARBONS From high temperature distillation of coal tar Heating petroleum at high temperature and pressure over a catalyst  POLYCYCLIC AROMATIC COMPOUNDS Aromatic compounds can have rings that share a set of carbon atoms (fused rings) Compounds from fused benzene or aromatic heterocycle rings are themselves aromatic  NAMING AROMATIC COMPOUNDS aniline = C6H5CH2CH2CH3 is aminobenzene) propylbenzene  NAMING AROMATIC COMPOUNDS C6H5NO2 = C6H5Br = nitrobenzene bromobenzene AROMATIC COMPOUNDS  THE PHENYL GROUP When a benzene ring is a substituent, the term phenyl is used (for C6H5 - ) ⚫ You may also see “Ph” or “φ” in place of “C6H5” “Benzyl” refers to “C6H5CH2”  DISUBSTITUTED BENZENES Relative positions on a benzene ring ⚫ ortho- (o) on adjacent carbons (1,2) ⚫ meta- (m) separated by one carbon (1,3) ⚫ para- (p) separated by two carbons (1,4)  DISUBSTITUTED BENZENES Relative positions on a benzene ring ⚫ ortho- (o) on adjacent carbons (1,2) ⚫ meta- (m) separated by one carbon (1,3) ⚫ para- (p) separated by two carbons (1,4)  NAMING BENZENES WITH MORE THAN TWO SUBSTITUENTS Choose numbers to get lowest possible values List substituents alphabetically with hyphenated numbers Common names, such as “toluene” can serve as root name (as in TNT) PHYSICAL PROPERTIES AND SOURCES  TEST FOR UNSATURATION The Baeyer test for unsaturation is for determining the presence of carbon-carbon double bonded compounds, called alkenes or carbon-carbon trible bonded compounds, called alkyne bonds. The Baeyer test uses dilute Pottasium Permanganate to Oxidize the carbon-carbon double or triple bond. It's called oxidation because the double bond is replaced by a hydroxy group (an OH group).  TEST FOR UNSATURATION The Baeyer test for unsaturation; SEAT WORK DRAW THE STRUCTURES FOR THE FF. AROMATIC COMPOUNDS 1) p-dibromobenzene 6) p-xylene 2) m-chloroaniline 7) m-bromophenol 3) p-bromotoluene 8) 1-bromo-2- ethylbenzene 4) 1-chloro-3,5-dimethyl 9) 3-methyl-2- benzene phenylhexane 5) o-chloroanisole 10) o-aminobenzoic acid