Alkyne combustion reaction: 2 C2H2 + 5 O2 4 CO2 + 2 H2O The combustion reactions are all exothermic. 180 Substitution Reactions 181 Substitution Reactions Reaction with chlorine: 182 Substitution Reactions Reaction with chlorine: CH4 + Cl2 CH3Cl + HCl chloromethane 183 Substitution Reactions Reaction with chlorine: CH4 + Cl2 CH3Cl + HCl chloromethane CH3Cl + Cl2 CH2Cl2 + HCl dichloromethane 184 CH2Cl2 + Cl2 CHCl3 + HCl trichloromethane 185 CH2Cl2 + Cl2 CHCl3 + HCl trichloromethane CHCl3 + Cl2 CCl4 + HCl tetrachloromethane 186 For organic reactions it is common practice to indicate the reaction conditions. That is, for the reaction with chlorine: 187 For organic reactions it is common practice to indicate the reaction conditions. That is, for the reaction with chlorine: CH4 + Cl2 CH3Cl + HCl 188 For organic reactions it is common practice to indicate the reaction conditions. That is, for the reaction with chlorine: heat (300 oC) CH4 + Cl2 CH3Cl + HCl 189 For organic reactions it is common practice to indicate the reaction conditions. That is, for the reaction with chlorine: heat (300 oC) CH4 + Cl2 CH3Cl + HCl or uv irrad. room temp. 190 Addition Reactions 191 Cl2 + H H C C H H dark 25 oC Cl Cl H H C C H H 1,2- dichloroethane 192 CH3CCH + 2 Cl2 propyne CH3CHCH2 + HBr propene CH3CCl2CHCl2 1,1,2,2-tetrachloropropane CH3CHBrCH3 2-bromopropane It turns out that when a hydrogen halide add to an alkene, the more electronegative halogen atom always tends to end up on the carbon atom of the double bond that has fewer hydrogen atoms (Markovnikov’s rule). 193 H2SO4 CH2CH2 + H2O CH3CH2OH 194 Hydrogenation The following reaction is an example of hydrogenation of an alkene, addition of H2 across a double bond. 195 H H H H C C H H ethene + H2 H C H C H H ethane 196 Functional Group Concept 197 Functional Group Concept A great many organic molecules have complex structures. 198 Functional Group Concept A great many organic molecules have complex structures. Trying to predict the properties and possible reactions of a complex structure can be very difficult. 199 Functional Group Concept A great many organic molecules have complex structures. Trying to predict the properties and possible reactions of a complex structure can be very difficult. Chemists have found it very useful to characterize certain well defined fragments of an organic molecule. 200 Functional Group Concept A great many organic molecules have complex structures. Trying to predict the properties and possible reactions of a complex structure can be very difficult. Chemists have found it very useful to characterize certain well defined fragments of an organic molecule. These fragments (in isolation) have well defined reactive capabilities. 201 When these units are found in complex structures, predictions can be made as to the likely properties and reactions of the complex structure. 202 When these units are found in complex structures, predictions can be made as to the likely properties and reactions of the complex structure. These fragment units are called functional groups. 203 Some common functional groups Functional group formula Name Example IUPAC Name Common Name 204 Some common functional groups Functional group formula Name Example IUPAC Name R O alcohol CH3OH methanol H Common Name methyl alcohol 205 Some common functional groups Functional group formula Name Example IUPAC Name R O alcohol CH3OH methanol R C H O O _ carboxylic CH3CO2H acid H ethanoic acid Common Name methyl alcohol acetic acid 206 Some common functional groups Functional group formula Name Example IUPAC Name R O alcohol CH3OH methanol R C H O O _ carboxylic CH3CO2H acid H Common Name methyl alcohol ethanoic acid acetic acid propanone acetone O R C R ketone CH3COCH3 207 Some common functional groups Functional group formula Name Example IUPAC Name R O alcohol CH3OH methanol R C H O O _ carboxylic CH3CO2H acid H Common Name methyl alcohol ethanoic acid acetic acid propanone acetone O R C R ketone CH3COCH3 R and R are alkyl (or more complicated groups). R cannot be H. R cannot be H for the alcohol (that would be water!), nor for the ketone (that would give an aldehyde). 208 Functional group formula Name Example IUPAC Name Common Name O R C aldehyde HCHO methanal formaldehyde H 209 Functional group formula Name Example IUPAC Name Common Name O R C aldehyde H R C O O R HCHO methanal formaldehyde ester CH3CO2CH2CH3 ethyl ethanoate ethyl acetate 210 Functional group formula Name Example IUPAC Name Common Name O R C aldehyde H R C O O R NH2 R HCHO methanal formaldehyde ester CH3CO2CH2CH3 ethyl ethanoate ethyl acetate amine CH3NH2 aminomethane methylamine 211 Functional group formula Name Example IUPAC Name Common Name O R C aldehyde H R C O O R NH2 R HCHO methanal formaldehyde ester CH3CO2CH2CH3 ethyl ethanoate ethyl acetate amine CH3NH2 aminomethane methylamine R and R are alkyl (or more complicated groups). R cannot be H (that would give an acid). R cannot be H for the amine (that would be ammonia!). 212 Functional group formula R O R Name ether Example IUPAC Name CH3OCH3 methoxymethane Common Name dimethyl ether 213 Functional group formula R R O Name Example IUPAC Name ether CH3OCH3 methoxymethane amide CH3CONH2 Common Name dimethyl ether O R C ethanamide NH 2 214 Functional group formula R R O Name Example IUPAC Name ether CH3OCH3 methoxymethane amide CH3CONH2 Common Name dimethyl ether O R C ethanamide NH 2 R and R are alkyl (or more complicated groups). R cannot be H (that would give an alcohol). R cannot be H for the ether (that would also give an alcohol). 215 Summary of name endings 216 Summary of name endings Functional group Parent alkane name ending 217 Summary of name endings Functional group Parent alkane name ending alcohol change e to ol 218 Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid 219 Summary of name endings Functional group Parent alkane name ending alcohol change e to ol carboxylic acid change e to oic acid ketone change e to one 220 Summary of name endings Functional group Parent alkane alcohol change e carboxylic acid change e ketone change e aldehyde change e to to to to name ending ol oic acid one al 221 Summary of name endings Functional group Parent alkane alcohol change e carboxylic acid change e ketone change e aldehyde change e amide change e to to to to to name ending ol oic acid one al amide 222 Summary of name endings Functional group Parent alkane alcohol change e carboxylic acid change e ketone change e aldehyde change e amide change e amine to to to to to name ending ol oic acid one al amide insert amino in front of alkane name 223 Summary of name endings Functional group Parent alkane alcohol change e carboxylic acid change e ketone change e aldehyde change e amide change e amine ester to to to to to name ending ol oic acid one al amide insert amino in front of alkane name insert alkyl name then change e to oate 224 Summary of name endings Functional group Parent alkane alcohol change e carboxylic acid change e ketone change e aldehyde change e amide change e amine ester ether to to to to to name ending ol oic acid one al amide insert amino in front of alkane name insert alkyl name then change e to oate change ane to oxy then add in second alkane name. 225 Key comment on a functional group The carboxylic acid is a combination of two functions groups: O C O C O H carboxylic acid ketone plus O H alcohol 226 Key comment on a functional group The carboxylic acid is a combination of two functions groups: O C O C plus O H carboxylic acid ketone HOWEVER, a compound such as O H alcohol 227 CH3CH2CCH2CH2 OH O would NOT function like a carboxylic acid, but as an alcohol in some reactions and a ketone in some other reactions. 228 Comparison of some properties 229 230 231 232 Some simple representative reactions of a few functional groups. 233 Formation of an ester: O CH3 C + CH3CH2OH O H carboxylic acid alcohol O CH3 C + H2O OCH2CH3 ester 234 Formation of an ester: O CH3 C + CH3CH2OH O H carboxylic acid alcohol ethanoic acid ethanol O CH3 C + H2O OCH2CH3 ester ethyl ethanoate 235 Oxidation of an alcohol: H2SO4,K2Cr2O7 CH3CH2OH alcohol warm 236 Oxidation of an alcohol: H2SO4,K2Cr2O7 CH3CH2OH alcohol O CH3 warm C H aldehyde 237 Oxidation of an alcohol: H2SO4,K2Cr2O7 CH3CH2OH alcohol O CH3 warm C H aldehyde further warming O carboxylic acid CH3 C O H 238 Note: In organic reactions, the side products (e.g. Cr3+ in the preceding reaction) are often not given. Here is the complete chemical equation: 239 Note: In organic reactions, the side products (e.g. Cr3+ in the preceding reaction) are often not given. Here is the complete chemical equation: 16 H+ + 2 Cr2O72- + 3 CH3CH2OH 4 Cr3+ +3CH3CO2H + 11 H2O 240 Note: In organic reactions, the side products (e.g. Cr3+ in the preceding reaction) are often not given. Here is the complete chemical equation: 16 H+ + 2 Cr2O72- + 3 CH3CH2OH (orange) 4 Cr3+ +3CH3CO2H + 11 H2O (green) 241 The intermediate reaction would be: 8 H+ + Cr2O72- + 3 CH3CH2OH (orange) 2 Cr3+ + 3 CH3CHO + 7 H2O (green) 242 Oxidation of an alcohol: OH CH3CHCH3 alcohol H2SO4,K2Cr2O7 or KMnO4 O CH3CCH3 ketone 243 Aromatic Compounds 244 Aromatic Compounds Aromatic – from aroma – a number of these compounds have strong and sometimes pleasant odors. 245 Aromatic Compounds Aromatic – from aroma – a number of these compounds have strong and sometimes pleasant odors. The most important compound in this family is benzene. 246 Benzene C6H6 This is a very important example in organic chemistry – an example of resonance: H H H C C C C H H C C H H H C H C C C C C H H H 247 The two resonance structures are averaged leading to the following structure: H H H C C C C C C H H H 248 If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to 249 If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to CH2 CH CH CH CH CH2 250 If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to CH2 CH CH CH CH CH2 1,3,5-hexatriene 251 If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to CH2 CH CH CH CH CH2 1,3,5-hexatriene This is not the case! 252 If resonance were not important for benzene, i.e. only one of the two preceding resonance structures were required to describe the structure of benzene, then we might expect benzene to have a reactivity similar to CH2 CH CH CH CH CH2 1,3,5-hexatriene This is not the case! 1,3,5-hexatriene is fairly reactive with a variety of reagents (e.g. HBr, Cl2, etc. in the dark). These reagents react only slowly with benzene. 253 Benzene is more stable than might be expected by examination of the individual resonance structures. 254 Naming benzene compounds Cl C H H C C C C C H H H 255 Naming benzene compounds Cl C H H C C C C C H H chlorobenzene H 256 Br C H H Br C C C C C H H 1,2-dibromobenzene 257 Br Br C H H Br C H C C C C C C C C C H H 1,2-dibromobenzene H C H Br H 1,3-dibromobenzene 258 Br Br C H H C H Br C C C C C C C C C H H H 1,2-dibromobenzene C H Br H 1,3-dibromobenzene Br C H 1,4-dibromobenzene H C C C C C Br H H 259 Br Br C H H C H Br C C C C C C C C C H H H o-dibromobenzene C H Br H m-dibromobenzene Br C H p-dibromobenzene H C C C C C Br H H 260 Br Br C H H C H Br C C C C C C C C C H H H o-dibromobenzene o = ortho m = meta p = para C H Br H m-dibromobenzene p-dibromobenzene Br C H H C C C C C Br H H 261 Steroids 262 263 264 IUPAC name (10R, 13R)-10,13-dimethyl-17-(6-methylheptan-2yl)-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1Hcyclopenta[a]phenanthren-3-ol 265 266 267 268 oral contraceptive 269 270 271 Theobromine (replace the CH3 at the arrow by H) is the stimulant found in 272 Theobromine (replace the CH3 at the arrow by H) is the stimulant found in chocolate. 273 274 275 276 Stereochemistry 277 Stereochemistry Stereochemistry: Deals with the 3dimensional arrangement of atoms in space for a particular chemical structure. 278 Stereochemistry Stereochemistry: Deals with the 3dimensional arrangement of atoms in space for a particular chemical structure. It also deals with how molecules react in 3dimensions. 279 Isomers 280 Isomers Two or more compounds with the same molecular formulas but different arrangements of the atoms in space. 281 Isomers Two or more compounds with the same molecular formulas but different arrangements of the atoms in space. Three different types of isomerism will be considered. 282 Isomers Two or more compounds with the same molecular formulas but different arrangements of the atoms in space. Three different types of isomerism will be considered. 1. Structural isomers (constitutional isomers) 283 Isomers Two or more compounds with the same molecular formulas but different arrangements of the atoms in space. Three different types of isomerism will be considered. 1. Structural isomers (constitutional isomers) 2. Geometric isomers 284 Isomers Two or more compounds with the same molecular formulas but different arrangements of the atoms in space. Three different types of isomerism will be considered. 1. Structural isomers (constitutional isomers) 2. Geometric isomers 3. Optical isomers 285 Structural isomers 286 Structural isomers Structural isomers (constitutional isomers): Compounds with the same molecular formulas but different arrangements of the atoms. 287 Structural isomers Structural isomers (constitutional isomers): Compounds with the same molecular formulas but different arrangements of the atoms. Example: Draw the structural isomers for C4H10 288 CH3CH2CH2CH3 butane 289 CH3CH2CH2CH3 butane CH3CHCH3 CH3 2-methylpropane (the 2 is redundant in this name) 290 Example: Draw the structural isomers for C5H12 291 Example: Draw the structural isomers for C5H12 CH3CH2CH2CH2CH3 pentane 292 Example: Draw the structural isomers for C5H12 CH3CH2CH2CH2CH3 pentane CH3CH2CHCH3 CH3 2-methylbutane (2 is redundant) 293 Example: Draw the structural isomers for C5H12 CH3CH2CH2CH2CH3 pentane CH3CH2CHCH3 2-methylbutane CH3 (2 is redundant) CH3 CH3CCH3 2,2-dimethylpropane CH3 (each 2 is redundant) 294 295 296 Example: Draw the structural isomers for C2H6O 297 Example: Draw the structural isomers for C2H6O CH3CH2OH ethanol 298 Example: Draw the structural isomers for C2H6O CH3CH2OH ethanol CH3OCH3 methoxymethane (dimethyl ether) 299 Exercise: Draw and name all the structural isomers for C6H14 (Answer there are 5). 300 Exercise: Draw and name all the structural isomers for C6H14 (Answer there are 5). The number of structural isomers increases significantly as the number of carbon atoms increases. For example, C20H42 has 366,319 isomers. 301 Number of carbons 1 2 3 4 5 6 7 8 9 10 20 30 40 Number of isomers for alkanes 1 1 1 2 3 5 9 18 35 75 366,319 4,111,846,763 62,491,178,805,831 302 Stereoisomerism 303 Stereoisomerism Stereoisomerism: Isomers having the same molecular formula and the same atom-toatom bonding, but the atoms differ in their arrangement in space. 304 Stereoisomerism Stereoisomerism: Isomers having the same molecular formula and the same atom-toatom bonding, but the atoms differ in their arrangement in space. Geometric isomers: Isomers having the same atom-to-atom bonding, but the atoms differ in their arrangement in space. 305 Examples: The trans and cis isomers of 1,2-dichloroethene. 306 Examples: The trans and cis isomers of 1,2-dichloroethene. H Cl C H C trans- 1,2-dichloroethene. Cl 307 Examples: The trans and cis isomers of 1,2-dichloroethene. H Cl C C H Cl Cl Cl C H C trans- 1,2-dichloroethene. cis- 1,2-dichloroethene. H 308 Examples: The trans and cis isomers of 1,2-dichloroethene. H Cl C C H Cl Cl Cl C H C H trans- 1,2-dichloroethene. (b.p. 48 oC , m.p. -50 oC) cis- 1,2-dichloroethene. (b.p. 60 oC , m.p. -80 oC) 309 An example from inorganic chemistry. NH3 Cl Pt NH3 Cl cis isomer NH3 Cl Pt Cl NH3 trans isomer 310 An example from inorganic chemistry. NH3 Cl Pt NH3 Cl cis isomer common name: cisplatin NH3 Cl Pt Cl NH3 trans isomer 311 An example from inorganic chemistry. NH3 Cl NH3 Cl Pt Pt NH3 Cl Cl NH3 cis isomer trans isomer common name: cisplatin Only the cis isomer is an effective chemotherapy agent. 312 Optical Isomers - Chirality 313 Optical Isomers - Chirality Polarized Light: Plane polarized light consists of electromagnetic waves with the electric component vibrating in one direction. 314 315 Optical Isomer: An isomer that causes rotation of the plane of polarization of light when passed through the substance. 316 317 Chiral (sounds like ki ral): An object that cannot be superimposed on its mirror image is called chiral. 318 319 Cl H H C C Cl Cl Cl Cl Cl 320 Cl H H C C Cl Cl Cl Cl Cl mirror plane 321 Cl H H C C Cl Cl Cl Cl Cl mirror plane Can superimpose these two molecules; trichloromethane is achiral. 322 F H H C C Br Cl Cl Br F mirror plane 323 F H H C C Br Cl Cl Br F mirror plane Cannot superimpose these two molecules; bromochlorofluoromethane is chiral. 324 Enantiomers: A chiral molecule and its nonsuperimposable mirror image are called enantiomers. 325 Enantiomers: A chiral molecule and its nonsuperimposable mirror image are called enantiomers. The simplest case is a tetrahedral carbon bonded to four different groups. 326 Enantiomers: A chiral molecule and its nonsuperimposable mirror image are called enantiomers. The simplest case is a tetrahedral carbon bonded to four different groups. Chiral molecules lack molecular symmetry. 327 328 HOOC H H C C OH HO CH 3 COOH CH 3 Lactic acid has optical isomers. 329 One optical isomer is sometimes represented by a D (for dextrorotatory: Latin dexter, right) if the rotation of the plane of polarization is to the right; or L (for levorotatory: Latin laevus, left), if the rotation of the plane of polarization is to the left. 330 One optical isomer is sometimes represented by a D (for dextrorotatory: Latin dexter, right) if the rotation of the plane of polarization is to the right; or L (for levorotatory: Latin laevus, left), if the rotation of the plane of polarization is to the left. The symbols + for rotation to the right and - rotation to the left, are also fairly commonly used. 331 One optical isomer is sometimes represented by a D (for dextrorotatory: Latin dexter, right) if the rotation of the plane of polarization is to the right; or L (for levorotatory: Latin laevus, left), if the rotation of the plane of polarization is to the left. The symbols + for rotation to the right and - rotation to the left, are also fairly commonly used. The lactic acid from muscle tissue is D-lactic acid or (+)-lactic acid. 332 A 50:50 mixture of the + and – isomers of the same compound is called a racemic mixture. There is no rotation of the plane of polarization for a racemic mixture. 333 Polymers 334 Polymer: (Greek: poly meros many parts) 335 Polymer: (Greek: poly meros many parts) Very large molecules with molar masses ranging from thousands to millions. 336 Polymer: (Greek: poly meros many parts) Very large molecules with molar masses ranging from thousands to millions. Applications: clothes, food packaging, appliances with plastic components, etc., etc., …. Plastics are polymers. 337 Two basic types of polymer: 338 Two basic types of polymer: 1. Thermoplastics: When heated these soften and flow, when cooled, they harden again. This process can be repeated. 339 Two basic types of polymer: 1. Thermoplastics: When heated these soften and flow, when cooled, they harden again. This process can be repeated. Examples: polyethylene and polystyrene 340 Two basic types of polymer: 1. Thermoplastics: When heated these soften and flow, when cooled, they harden again. This process can be repeated. Examples: polyethylene and polystyrene 2. Thermosetting plastics: When first heated they are plastic, but further heating forms a highly cross-linked structure. Cannot be softened by reheating. 341 Two basic types of polymer: 1. Thermoplastics: When heated these soften and flow, when cooled, they harden again. This process can be repeated. Examples: polyethylene and polystyrene 2. Thermosetting plastics: When first heated they are plastic, but further heating forms a highly cross-linked structure. Cannot be softened by reheating. Example: formica. 342 Monomers: The small (low molar mass) molecules used to synthesize polymers. 343 Synthetic Polymers 344 Synthetic Polymers Two principal reaction types: Addition and condensation. 345 Synthetic Polymers Two principal reaction types: Addition and condensation. Addition Polymers: Made by monomer units directly joining together. 346 Synthetic Polymers Two principal reaction types: Addition and condensation. Addition Polymers: Made by monomer units directly joining together. Condensation Polymers: Made by monomer units combining so that a small molecule, usually water, is split out. 347 Addition Polymers 348 Addition Polymers The monomer for addition polymers normally contains one or more double bonds. 349 Addition Polymers The monomer for addition polymers normally contains one or more double bonds. The polymerization reaction is initiated using an organic peroxide. 350 Addition Polymers The monomer for addition polymers normally contains one or more double bonds. The polymerization reaction is initiated using an organic peroxide. R O O R R O . + .O R 351 Addition Polymers The monomer for addition polymers normally contains one or more double bonds. The polymerization reaction is initiated using an organic peroxide. R O O R R O . + .O R organic peroxide free radicals 352 Initiation step: H H C H C H + .OR H .C H H C OR H 353 Initiation step: H H C H C H + .OR H .C H H C OR H 354 Then H C H H H H H C .C H C OR H H H .C H C H OR C H H 355 Etcetera: H (H H C C ) H n where n would typically range from 1000 to 50,000. 356 Different experimental conditions give different polymers. H _ _ CH 2 CH 2 _ C _ CH 2 _ RCH 2CH 2 H 357 Different experimental conditions give different polymers. H _ _ CH 2 CH 2 _ C _ CH 2 _ RCH 2CH 2 H 358 Different experimental conditions give different polymers. H _ _ CH 2 CH 2 _ C RCH 2CH 2 H _ CH 2 _ _ _ _ CH 2 CH 2 CH _ CH 2 _ CH 2 CH 2 + H R 359 Different experimental conditions give different polymers. H _ _ CH 2 CH 2 _ C RCH 2CH 2 H _ CH 2 _ _ _ _ CH 2 CH 2 CH _ CH 2 _ CH 2 CH 2 + H R branched polymer chain 360 Cross linked polymers are formed in the following manner: _ _ _ CH 2 CH 2 CH H _ CH 2 _ R RO 361 Cross linked polymers are formed in the following manner: _ _ _ CH 2 CH 2 CH H _ CH 2 _ R RO _ _ _ CH 2 CH 2 C H _ CH 2 _ 362 Cross linked polymers are formed in the following manner: _ _ _ CH 2 CH 2 CH H _ CH 2 _ R RO _ _ _ CH 2 CH 2 C H H H _ CH 2 _ H C C H 363 Cross linked polymers are formed in the following manner: _ _ _ CH 2 CH 2 CH H _ CH 2 _ R RO _ _ _ CH 2 CH 2 C H H H _ CH 2 _ H C C H 364 Cross linked polymers are formed in the following manner: _ _ _ CH 2 CH 2 CH H _ CH 2 _ R _ RO _ _ CH 2 CH 2 C H H _ CH 2 _ H C C H H _ _ _ CH 2 CH 2 CH _ CH 2 _ CH 2 C H2 365 _ _ _ CH 2 CH 2 CH _ CH 2 _ CH 2 C H2 _ _ CH 2 _ _ CH 2 C H CH _ 2 366 _ _ _ CH 2 CH 2 CH _ CH 2 _ CH 2 C H2 _ _ CH 2 _ _ CH 2 C H CH _ 2 _ _ _ CH 2 CH 2 CH _ CH 2 _ CH 2 _ _ _ CH 2 CH 2 CH 2 CH _ CH 2 _ 367 _ _ _ CH 2 CH 2 CH _ CH 2 _ CH 2 C H2 _ _ CH 2 _ _ CH 2 C H CH _ 2 _ _ _ CH 2 CH 2 CH _ CH 2 _ CH 2 cross linked polymer _ _ _ CH 2 CH 2 CH 2 CH _ CH 2 _ 368 Polyethylene is the most widely used polymer. 369 Polyethylene is the most widely used polymer. The long linear chain version is called high density polyethylene (HDPE) (d = 0.97 g/ml). 370 Polyethylene is the most widely used polymer. The long linear chain version is called high density polyethylene (HDPE) (d = 0.97 g/ml). It is hard, tough, and rigid. Used for milk and detergent containers. 371 The branched chain version is called low density polyethylene (LDPE) (d=0.92 g/ml). The branched chains of polyethylene prevent close packing – hence the density is lower. 372 The branched chain version is called low density polyethylene (LDPE) (d=0.92 g/ml). The branched chains of polyethylene prevent close packing – hence the density is lower. This polymer is soft and flexible. Used for grocery bags, bread bags, etc. 373 The cross linked polymer is called cross-linked polyethylene (CLPE). This is a very tough material. Used for plastic caps on soft drink bottles. 374 375 Condensation Polymers 376 Condensation Polymers A condensation reaction occurs when two molecules react by splitting out or eliminating a small molecule such as water. 377 Ester formation reaction: CH3CO2H + CH3CH2OH acetic acid ethanol CH3CO2CH2CH3 + H2O ethyl acetate Polyesters O O C C 2 H O terephthalic acid O O H O H +2 H _ O _ CH 2 _ CH 2 _ O _ H ethylene glycol O C C _ _ _ _ O CH 2 CH 2 O O _C +2 H2O O C O CH 2 CH 2 O H 379 Polyesters O O C C 2 H O terephthalic acid O O ethylene glycol O C H O H +2 H _ O _ CH 2 _ CH 2 _ O _ H C _ _ _ _ O CH 2 CH 2 O O _C +2 H2O O C O CH 2 CH 2 O Now consider another terephthalic acid molecule reacting with the indicated alcohol functional group. H 380 O O C O C _ _ _ _ O CH 2 CH 2 O _ n This is an example of the repeat unit for a polyester. In this case it is poly(ethylene terephthalate) called PET. 381