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 H s (298 K) =  H v (298 K) +  H fus (298 K) We have discussed methods to estimate  H v (298 K); are there any ways to estimate  H fus (298 K) or.

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Presentation on theme: " H s (298 K) =  H v (298 K) +  H fus (298 K) We have discussed methods to estimate  H v (298 K); are there any ways to estimate  H fus (298 K) or."— Presentation transcript:

1  H s (298 K) =  H v (298 K) +  H fus (298 K) We have discussed methods to estimate  H v (298 K); are there any ways to estimate  H fus (298 K) or  H fus (T fus ) ? Walden’s Rule:  H fus (T fus ) / T fus = 54.4 J mol -1 K -1

2 Figure. Fusion enthalpies as a function of the number of methylene groups of the n-alkanes.

3 Figure. Total phase change enthalpy of the n-alkanes as a function of the number of methylene groups.

4 Figure. Total phase change entropy of the n-alkanes as a function of the number of methylene groups.

5 Fusion enthalpies as a function of the number of methylene groups (N) of the n-alkanes.  H fus (T fus ) = (2929±178)N - (3281±13006); r 2 = 0.8823 Total phase change enthalpies as a function of the number of methylene groups (N) of the n-alkanes.  H fus (T fus ) = (3552±80)N + (972±5868); r 2 = 0.9818 Total phase change entropy as a function of the number of methylene groups (N) of the n-alkanes.  S fus (T fus ) = (9.027±0.25)N + (45.1±18.44); r 2 = 0.9725

6 Table. Contributions by the hydrocarbon portion of acyclic and aromatic molecules Acyclic and Aromatic Carbon Groups Group Value G i, Group Coefficient C i J. mol -1. K -1 primary sp 3 C CH 3 - 17.6 secondary sp 3 C>CH 2 7.11.31 a tertiary sp 3 C-CH<-16.40.60 quaternary sp 3 C>C<-34.80.66 secondary sp 2 C=CH 2 17.3 tertiary sp 2 C=CH- 5.30.75 quaternary sp 2 C=C(R)--10.7 tertiary sp CH-C  14.9 quaternary sp C-C  -2.8 aromatic tertiary sp 2 C=C a H- 7.4 quaternary aromatic sp 2 C adjacent to an sp 3 atom=C a (R)- -9.6 peripheral quaternary aromatic sp 2 C adjacent to an sp 2 atom=C a (R)- -7.5 internal quaternary aromatic sp 2 C adjacent to an sp 2 atom=C a (R)- -0.7 a The group coefficient of 1.31 for is applied only when the number of consecutive methylene groups equals or exceeds the sum of the remaining groups; R: any alkyl or aryl group unless specified otherwise

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8 Estimations of acyclic and aromatic hydrocarbons Examples: ethylbenzene:  H fus (T fus ) = 9.16 kJ mol -1 ; T fus = 178.2 K octylbenzene:  H fus (T fus ) = 29.96 kJ mol -1 ; T fus = 234.2 K 4-methyl-1-pentene:  H fus (T fus ) = 4.93 kJ mol -1 ; T fus = 118.9 K

9 Table. Functional groups dependent on the substitution patterns Functional Groups Group Value (G k ) Group Coefficient (C k ) J/(mol -1 K -1 ) Total number of functional groups in the molecule: k; G k k = 2 3 4 5 6 chlorine R-Cl 10.8 1.5 1.5 1.5 1.51.5 2-fluorines on an sp 3 CR-CF 2 -R 13.2 1.06 1.06 1.06 1.061.06 hydroxyl group R-OH 1.7 10.4 9.7 13.1 12.113.1 carboxylic acid R-C(=O)OH 13.4 1.21 2.25 2.25 2.252.25 R: any alkyl or aryl group unless specified otherwise;

10 Table. Contributions of the remaining functional groups Functional Groups a Abbreviated Structure Group Value (G k ) a, J/(mol -1 K -1 ) bromine R-Br17.5 fluorine on an sp 2 carbonR 2 -CHF19.5 fluorine on an aromatic carbon=CF-16.6 3-fluorines on an sp 3 carbonCF 3 -R13.2 1-fluorine on an sp 3 carbonR-CF-(R) 2 12.7 fluorine in perfluorinated compounds b C n F 2n+2 15.2 one fluorine on a ring carbon -CHF-; 17.4 two fluorines on a ring carbon-CF 2 -[17.5] iodineR-I19.4 phenol =C-(OH)-20.3 ether R-O-R4.71 aldehydeR-CH(=O)21.5 ketone R-C(=O)-R4.6 ester R-C(=O)O-R7.7 aromatic heterocyclic amine =N-[10.9] acyclic sp 2 nitrogen =N-[-1.8] tertiary amineR-N(R 2 )-22.2 secondary amineR-NH-R-5.3 primary amineR-NH 2 21.4 nitro group R-NO 2 17.7

11 Table. Contributions of the remaining functional groups Functional Groups a Abbreviated Structure Group Value (G k ) a, J/(mol -1 K -1 ) azoxy nitrogenN=N(  O)-[6.8] nitrile R-C  N17.7 isocyanideR-NC[17.5] tertiary amidesR-C(=O)NR 2 -11.2 secondary amides R-C(=O)NH-R1.5 primary amide R-CONH 2 27.9 N,N-dialkylformamideHC(=O)NR 2 [6.9] sulfidesR-S-R2.1 disulfides R-SS-R9.6 thiols R-SH23.0 a R: any alkyl or aryl group unless specified otherwise; values in brackets are tentative assignments; all group coefficients can be assumed to be 1; the functional groups are in bold;

12 Estimations of acyclic and aromatic hydrocarbon derivatives Examples: 3-heptanone:  H fus (T fus ) = 17.53 kJ mol -1 ; T fus = 236 K p-  -cumylphenol:  H fus (T fus ) = 21. 68 kJ mol -1 ; T fus = 346.4 K 2,3,4,5-tetrachlorobiphenyl:  H fus (T fus ) = 25.2 kJ mol -1 ; T fus = 363.9 K

13 Estimations of cyclic hydrocarbons

14 Examples: cyclohexylbenzene:  H fus (T fus ) = 15.3 kJ mol -1 ; T fus = 280.5 K adamantane:  H fus (T fus ) = 10.9 kJ mol -1 ; T fus = 541.2 K;  H tran (T trans ) = 3.38; T trans = 208.6 K fluorene:  H fus (T fus ) = 19.58 kJ mol -1 ; T fus = 387.9 K

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16 Estimations of cyclic hydrocarbon derivatives C 27 H 46 O cholesterol  H fus (T fus ) = 27.41 kJ mol -1 ; T fus = 420.2 K;  H tran (T trans ) = 2.5; T trans = 304.8 K

17 Estimate  S tpce (T fus ) of dibenzothiophene T fus 373.2  H fus (T fus ) 21.6 kJ mol -1 Estimate  S tpce (T fus ) of C 11 H 16 N 4 O 2 8-butyltheophylline T fus 509.2  H fus (T fus ) 32.3 kJ mol -1 theophylline

18  -D-glucose T fus =432.2 K  fus H m = 34.3 kJ mol -1 l-menthol T fus =316.2 K  fus H m = 11.88 kJ mol -1

19 1-chlorodibenzodioxin T fus = 378.2 K  fus H m = 23.2 kJ mol -1 phenazine T fus = 450.2 K  fus H m = 20.92 kJ mol -1

20 Octyl methacrylate T fus = 230.3 K  fus H m = 24.9 kJ mol -1 2-n-propy1-5-(4-bromophenyl)thiophene T fus = 360.4 K  fus H m = 15.7 kJ mol -1

21 How good are these parameters at estimating  S tpce (T fus )? Fig. A comparison of the experimental and calculated total phase change entropies of 2637 compounds. The area between the two lines represents  2 .

22 Fig. A histogram of the distribution of errors in (exp) - (calc) for the database compounds of Fig. 1. Each interval represents one standard deviation (15.3 J. mol -1. K -1 ).

23 Applications of Group Values Used to Calculate  S tpce (T fus ) Although polymers are not completely crystalline, they can be made highly crystalline and they have a melting temperature associated with their melting. The degree of crystallinity can be determine by X-Ray crystallography.

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25 Estimated Total Phase Change Entropy for Some Polymers

26 Table. Molar Transition Enthalpies (kJ mol -1 ) and Entropies (J mol -1 K -1 ) of Select Amphiphilic Semiperfluorinated-Semiper- hydrogenated Diblock and Triblock Organic Compounds a T(K)  H pce  S pce  S tpce 0.6  S tcpe  S tcpe  H tpce  H tpce exptcalcd calcd exptcalcd UNSUBSTITUTED DIBLOCK MOLECULES C 16 H 9 F 25 F 3 C(CF 2 ) 11 (CH 2 ) 4 H 147.0 0.7 5 314.0 1.4 4 349.021.06169.457.193.6 23.119.9 C 16 H 13 F 21 F 3 C(CF 2 ) 9 (CH 2 ) 6 H 306.0 4.214 318.016.9536761.6 100.921.119.6 C 16 H 17 F 17 F 3 C(CF 2 ) 7 (CH 2 ) 8 H 301.29.531.6 303.25.718.850.390.2 147.9 15.227.3 C 17 H 21 F 15 (CF 3 ) 2 CF(CF 2 ) 4 (CH 2 ) 10 H 220.0 313.6 261.01869.082.684.6 138.621.018.9

27 T(K)  H pce  S pce  S tpce 0.6  S tcpe  S tcpe  H tpce  H tpce exptcalcd calcd exptcalcd C 18 H 13 F 25 F 3 C(CF 2 ) 11 (CH 2 ) 6 H 164.0 0.5 1 316.0 3.511 357.023.465.579.765.7 107.827.423.5 C 18 H 21 F 17 F 3 C(CF 2 ) 7 (CH 2 ) 10 H 288.0 3.512 308.020.26577.786.8 142.323.726.9 C 19 H 21 F 19 (CF 3 ) 2 CF(CF 2 ) 6 (CH 2 ) 10 H 274.0 1 3.6 298.02583.987.584.6 138.62622.1 C 20 H 17 F 25 F 3 C(CF 2 ) 11 (CH 2 ) 8 H 192.0 2.412.5 329.0 6.419.5 361.023.765.797.674.712232.526.9 C 20 H 21 F 21 F 3 C(CF 2 ) 9 (CH 2 ) 10 H 317.0 4.012 337.024.4728578.9 129.328.426.6

28 Figure. A comparison of calculated and experimental total phase change entropies for the partially fluorinated amphiphilic compounds.

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