- Email: [email protected]
Dielectric relaxation mechanism and internal rotation in phenylpyridines
CIIE\lICAL
Volume 108. number ?
DIELECTRIC
RELAXATION
13 July 1984
PHYSICS LISTTERS
hi ECHANISM AND INTERNAL
ROTATION
IN PHENYLPYRIDINES Piotr FREUNDLICH, Hubert A. KOtODZIEJ. Edward NAREWSKI It~sf_srltr Chcrttii. L:ltiwcrsyfer Ii’roc?aIvski. 50-363 ll’ru&w. Poland and Salvatore
SORRlSO
Drparf ittirttm
di 0tiittica.
.!hit*crsitli di Pcrtt.via. 06100
Pcrtrgia. Ital>
I_ Introduction
can
hlolecular dynaniics investigations by means of dielectric relasation nicasurcn~ents in nwlecules in which internal rotation is possible continue to be undcrtakcn by a number using both theoretical The contribution from tion of this interesting
of research workers [I-l 21. and cspcrhnental approaches. our laboratory to the clucidaproblem has shown rhat, in
general. the Goulon-Rivail model [4] ca11 be employed in this case to describe the dynzunics of the dielectric relrtuation process. This was found to be coninlon to many molecular structures for which the internal rotation does not possess the same charactcr-
ring nionxnt. Thus, taking into account that this phcnyl group rnonient changes with a change in the dihedral angle between the two rotating planes, one
Physics
Publishing
Division)
behviour
for
this
type
of mol-
The 2-phenylpyridine and 3-phenylpyridinc were commercial products (Janscn Chemicals) purified by means of micro-distillation under vacuunl. The I>-xylene used as solvenr was dried over nlcrallic sodium and distilled, Its purity was chcckcd by measuring the static dielectric pcmittivity at 298 K. The dielectric permittivity (E’) and loss (E”) were
the phcnyl ring derives essentially from both the mesomcric effect and the moment induced by the pyridinc
(North-Holland
a peculiar
2. Esperhental
istics [for example, bipyridyls. dipyridylcthylenes. benzoyl(diazo)plienylmcttialle and dibenzoyl]. A COI~I~OI~ peculiarity of these substrates arises front the presence of group nionicnts rotating with respect to each 0111cr. Phenylpyridines way also contain two such rotating groups. However, in this case, the partial moment of
0 009-26 14/84/S 03 -00 0 Elsevier Science Publishers
forrscc
cculc, knowledge of which would improve our information on the niolecular dynamics. With this aim. the dielectric dispersion of 2- and j-phenylpyridines was measured in a non-polar solvent, at four tempcraturcs and at xarious frequencies in the GHz region. It should be noted that the conformational aspects (to which the dynamics is strictly related) of adjacent aromatic systems are still 311 object of debate anlong researchers using both the phorophysical and the photochenkzd approaches [ 1Z-1 7] _
B.V.
nwasurcd in the frequency range 2-l 0 GHz by means of an Orion coaxial slotted line type EZN-1 for 2-3 GHz and Unipan K-I 00 and PIT 4.5 laboratory systenx for 4-l 0 GHz [ 1 S]. Static dielectric perniittivitl 373
Volunw 108. was mcasurcd
nun’ bcr 4
41 1 S9 kHz using a TESLA
BM 484
aurobalance b,idge. All mcasuremcnts were made at four tcmpcrr .urcs (393. 303. 313 and 323 K), the tcnlpcrature bell i: controlled by mcms of a Unipan 336 PID (proporiional-integral-differential) tcmperaturc conrroller with a precision of 0.01 K over the entire nmsurcnwnt range. The cxpcrimcntal errors in the dielectric parauictcrs wcrc +2 and +3% for 15’and E”, respcclively.
13 July 19&l
CHEXlICAL PliYSlCS LI:TTl:RS 3. Results and discussion The results mxsurcmmts
phcnylpyridhc also these
SI~OWII
as
figures,
both molcculcs cast.
obtained for both
from
the diclcctric
2-phtnylpyridinc
rclssation
(IPP)
and 3-
(3PP) arc collected in tabic 1. and are Cole-Cok plots in figs. 1 and 3. From one can see that the relwation display
a certain
distribution.
Ihc equaIion
E(iO) = 12, + (E,, - E,)/[
1 + (iwi-)l-a]
.
times in
of
this
13 July 1984
CHEMICAL PHYSICS LETTERS
Volunw 108, munbcr 4
010
323
K
E-
I’
!. ---_.
i -...__
O.lOt_
,:
i 0.10 E’ 0.05
I
303
-----.__._ ,_=
-
293
/------~_,
‘_.
.I.
‘\
\
.\
cm be used. where a is the distribution paramerer for the dielectric relaxation times. the values of which are in tab!e 7 (see also fig. 3). Ir should be noted that the value of cxclearly decreases with increasing
shown
telnperature.
Table 2 Obscrvcd
nnd c3lculatcd di&crric pammcters mol P-l, rcspectivcly 3)
for 3-phcnyipyridinc
(3PP) and 2-phcnylpyridinc
(ZPP) in
/J-SykIlC
31
concentrations
of&31 7 ;Ind 0.319 1somLY
T(K)
TObS (1~s)
r,(-gb)
3PP
193 303 313 323
74.08 21.01 ‘0.43
11.63
0.11
2.28
1.5-M
2.54s
7 373 -.__
ZO.SO
0.11
2.25
2.515
7.5 14
2.309
19.42
0.04
2.12
1.366
1.486
2.309
19.50
lS.65
0.03
2.04
1.457
2.449
2.300
193 303 313
23.03 26.17 23.90
27.47 -_ ‘5 .60 23.50
0.09 0.07 0.05
1.86 1.82 1.75
1.466 2.440 1.411
2.46-I 2.440 1.410
7.29s
323
22.04
21.75
0.03
1.68
2.394
2.395
2.290
21’P
(ps)
0.
v W)
(co)obs
ko)~lc
EC0
2.319 2.793
ac3) The nctivntion cnthnlpy (tifg in kJ mol-‘) was 3.9 2 1.2 and 4.1 2 I.2 for 3PP and ZPP, rcspccti$%?ly. It V.X calcuhrcd cording to Ilgring‘s equation 1191,shown in fig: 3. b) rp~p is the rclns~rion time chxhtcd by mcctns of rho Chum-Powlcs relationship [ 191 7&p = [ (~EIJ+ EW.)/~EOITO~~
375
I3 July 1984
CHEhlICAL PHYSICS LISTTI:RS
Volw:w 108, nunlbcr 4
-logTZ
8.2c
8.15
8.1C
3.10
3.20
3.30
3.40 +Ox
l‘llc dielectric KlilSiltioIl xcordin~ to the equation:
tiines
(7) wcrc calculated
. 1 - (Y. Such ;I distribution of rclasution times in these ~noleculcs could be due to tltc overlapping oi’ two or I~WC bands. Howcvcr, regarding the interpretation of the nwchanisn~ of the diclcctric relaxation process in tl~csc molecules. out can say tllat , 35 in previous sitnilar situations. it is quite difficult IO justify the
where
p =
prcscnce
376
of nwc
than IWO
absorption bands 3s cm-
poncn~s of rhc cornplcs band observed csperimcntally. In rhcory, tltcsc two overIapping absorptions may bc due to: (i) 111e two co~npo~~n~s (along the mutually pcrpcndicular n~olccular rotation axes) of the molecular clcctric dipole moment. assuming the molecule IO be ripid: or (ii) a fast intercovcrsion between IWO rotamers srabilised the 7; colljugation. which nx~y give rise to the appcarancc of an additional mechanism _ In both molccuics invcstigatzd. there exist two colllpollenls of the electric dipole moment. One of tllc Conq~oncnts is parallcl to the longest axis of tllc I~~OlCcUlC(SW fig.
4) and the other is perpendicular
to it. If we assunie tile presence of rigid configurations, WC can obtain 1I (tbc nlonlent of inertia connected with rotation around tiles and?* axes) and II (the moment of inertia connected with the s and z axes)
I, = $(f_\-+I:).
+I,*),
References [ 11 J. Coulon.
G. Roussy.
51. ilollcckcr.
31.X1.Claudon.
G.W. Chsntry aud E-4. Nicol, Mol. Ph\*s. 33 (1977)
377. D. Gnnct. 31. Evans and G.J. Davies. 5101. PI1ys. 30 (1971) 973. A. &do, E. Fischrr and S. hljyamoto. Phys. 2. 30 (1939) 377. J. Goulon and J.K. Rivail. Spcc~roscopir Conscquenws of Very Fast Ch~niical Processes. in: Protons and ions involved in fast dynamic Phenomena. cd. P. Laszlo (I%xicr. Amsterdxll. 197s). D.D. I&p. D.Ii. IhnbuhcI and N’.E. Vauphn. J. Chem. Phys. 50 (1969) 3904. C. N’iIIi~ms 2nd Xl. Cook. Trxns. lirx!xy Sot. 67 (1971) J. Coulon,
by using rhe relations I, = :&.
I3 July 1984
CHIShlICAL PHYSICS LETTERS
Volume 1 OS. nunibcr 4
(3)
\vlwrc lx, lJ. and I_ arc the nionwnts of inertia for the rotation around the adds. _Vand z. On this basis, one cm cspcct tile existence of two different dielectric relaxation times 7I and 7-)_ From the calculation of the rnonxnt of inertia. OIL ~911 easily obtain the ratio of the relaxation times:
990. 7I/72 which
= (/t//#) appears
= 1 .x
.
to bc the same
(4) for botll
isomers
csnmin-
cd. Tllis is the tltcorcricxl ratio calculated frotn the asswnption that thcsc niolcculcs arc rigid. Front the above value and tile values of the sanx ratio reported previously [I 0.1 1 ] _it could be suggested that. in this case. tlx diffcrcnce between the relaxathe espcdtion times 71 and 7, is too small to induce 1nc111aI1y observed distribution. TAGn~ into consideration the decrease
C. Bror,
\lolcculsr
moliuns
in liquids.
cd. J. Lascomb
(Rcidcl. Dordrccht. 1974). 1’. Frcundliclr. E. Jakuwk. IIA. KoYodTicj. A. KoII. 51. P;?jdowska and S. Sorriso. J. P!rys. Ciwm. 57 (1963) 103-l. A. Koll. I1.A. Kohdzicj and S. Sorho_ 2. Physik. Chcm. XI-. 134 (1963) 163. E. Jakusck. P. Frcundlich. 14.X. Kohdzicj and S. Sorriso. ChClll. Phys. Sl (19S3) 153. E. Jakusck. P. I~rcundlirl~. 1i.X. IiurCldi?icj. A. Koll md
Sorriso. Clicm. 1%)‘~.64 (196-l) 141. G. Xlarconi. G. Orlandi and G. Poypi. J. Photochcm. S.
tive dipole nionient with an increase in tentperature and a fidir activation cntimlpy (table 2). one could say that there is probably a fast intcrcoversion. In conclusion, these results exclude the presence of a sitnple mechanism for the dielectric relaxation process of both isonxrs. However. they are unable to distinguish between the possibilities (i) and (ii). T’his aspect is bcin, 0 studied furhtcr in our laboratory.
19 (19SZ) 329. E. Fisher, J. Photochcm. 17 (1961) 331. G. Orhndi. G. Posei 2nd G. Marconi. J. Chem. Sot. Farad;ly I1 17 (19SO) 59s. F. Xlasctti. G. Bartocci and U. 1lszzuc;lto. CZIZZ. Chim. 1131. I12 (19SZ) 255. G. Bartocci. 1:. Masctti. U. JIaz~uc~to. S. Dclloutc and G. Orhndi. Spcctrochim. Acra 36A (1961) 729. G. Bxtwxi and U. M~zzuuro. J. Lumincsccncc 27 (1962) 163. [ 161 H.A. Eutodzicj. 11. Pajdo\vska and L. Sobczyk. J. Phys.
Acknowledgeement
E. I1 (1970 752. [ 191 N.E. ltill. W.E. V;tuplxm. A.15 Price and 11. hvics. Diclcctric propcrtics and molccuhr bclraviour <\‘nn Nnstmnd, Princeton. 1969).
of tlw tffec-
WC tltank Dr. E. Jakusck for valuable discussions. Grateful acknowledgement is also nladc to the Polish Academy of Sciences and to the Consiglio Nazionalc dellc Rccrchc (Rome) for financi;ll support.
377
Volume 108. number ?
DIELECTRIC
RELAXATION
13 July 1984
PHYSICS LISTTERS
hi ECHANISM AND INTERNAL
ROTATION
IN PHENYLPYRIDINES Piotr FREUNDLICH, Hubert A. KOtODZIEJ. Edward NAREWSKI It~sf_srltr Chcrttii. L:ltiwcrsyfer Ii’roc?aIvski. 50-363 ll’ru&w. Poland and Salvatore
SORRlSO
Drparf ittirttm
di 0tiittica.
.!hit*crsitli di Pcrtt.via. 06100
Pcrtrgia. Ital>
I_ Introduction
can
hlolecular dynaniics investigations by means of dielectric relasation nicasurcn~ents in nwlecules in which internal rotation is possible continue to be undcrtakcn by a number using both theoretical The contribution from tion of this interesting
of research workers [I-l 21. and cspcrhnental approaches. our laboratory to the clucidaproblem has shown rhat, in
general. the Goulon-Rivail model [4] ca11 be employed in this case to describe the dynzunics of the dielectric relrtuation process. This was found to be coninlon to many molecular structures for which the internal rotation does not possess the same charactcr-
ring nionxnt. Thus, taking into account that this phcnyl group rnonient changes with a change in the dihedral angle between the two rotating planes, one
Physics
Publishing
Division)
behviour
for
this
type
of mol-
The 2-phenylpyridine and 3-phenylpyridinc were commercial products (Janscn Chemicals) purified by means of micro-distillation under vacuunl. The I>-xylene used as solvenr was dried over nlcrallic sodium and distilled, Its purity was chcckcd by measuring the static dielectric pcmittivity at 298 K. The dielectric permittivity (E’) and loss (E”) were
the phcnyl ring derives essentially from both the mesomcric effect and the moment induced by the pyridinc
(North-Holland
a peculiar
2. Esperhental
istics [for example, bipyridyls. dipyridylcthylenes. benzoyl(diazo)plienylmcttialle and dibenzoyl]. A COI~I~OI~ peculiarity of these substrates arises front the presence of group nionicnts rotating with respect to each 0111cr. Phenylpyridines way also contain two such rotating groups. However, in this case, the partial moment of
0 009-26 14/84/S 03 -00 0 Elsevier Science Publishers
forrscc
cculc, knowledge of which would improve our information on the niolecular dynamics. With this aim. the dielectric dispersion of 2- and j-phenylpyridines was measured in a non-polar solvent, at four tempcraturcs and at xarious frequencies in the GHz region. It should be noted that the conformational aspects (to which the dynamics is strictly related) of adjacent aromatic systems are still 311 object of debate anlong researchers using both the phorophysical and the photochenkzd approaches [ 1Z-1 7] _
B.V.
nwasurcd in the frequency range 2-l 0 GHz by means of an Orion coaxial slotted line type EZN-1 for 2-3 GHz and Unipan K-I 00 and PIT 4.5 laboratory systenx for 4-l 0 GHz [ 1 S]. Static dielectric perniittivitl 373
Volunw 108. was mcasurcd
nun’ bcr 4
41 1 S9 kHz using a TESLA
BM 484
aurobalance b,idge. All mcasuremcnts were made at four tcmpcrr .urcs (393. 303. 313 and 323 K), the tcnlpcrature bell i: controlled by mcms of a Unipan 336 PID (proporiional-integral-differential) tcmperaturc conrroller with a precision of 0.01 K over the entire nmsurcnwnt range. The cxpcrimcntal errors in the dielectric parauictcrs wcrc +2 and +3% for 15’and E”, respcclively.
13 July 19&l
CHEXlICAL PliYSlCS LI:TTl:RS 3. Results and discussion The results mxsurcmmts
phcnylpyridhc also these
SI~OWII
as
figures,
both molcculcs cast.
obtained for both
from
the diclcctric
2-phtnylpyridinc
rclssation
(IPP)
and 3-
(3PP) arc collected in tabic 1. and are Cole-Cok plots in figs. 1 and 3. From one can see that the relwation display
a certain
distribution.
Ihc equaIion
E(iO) = 12, + (E,, - E,)/[
1 + (iwi-)l-a]
.
times in
of
this
13 July 1984
CHEMICAL PHYSICS LETTERS
Volunw 108, munbcr 4
010
323
K
E-
I’
!. ---_.
i -...__
O.lOt_
,:
i 0.10 E’ 0.05
I
303
-----.__._ ,_=
-
293
/------~_,
‘_.
.I.
‘\
\
.\
cm be used. where a is the distribution paramerer for the dielectric relaxation times. the values of which are in tab!e 7 (see also fig. 3). Ir should be noted that the value of cxclearly decreases with increasing
shown
telnperature.
Table 2 Obscrvcd
nnd c3lculatcd di&crric pammcters mol P-l, rcspectivcly 3)
for 3-phcnyipyridinc
(3PP) and 2-phcnylpyridinc
(ZPP) in
/J-SykIlC
31
concentrations
of&31 7 ;Ind 0.319 1somLY
T(K)
TObS (1~s)
r,(-gb)
3PP
193 303 313 323
74.08 21.01 ‘0.43
11.63
0.11
2.28
1.5-M
2.54s
7 373 -.__
ZO.SO
0.11
2.25
2.515
7.5 14
2.309
19.42
0.04
2.12
1.366
1.486
2.309
19.50
lS.65
0.03
2.04
1.457
2.449
2.300
193 303 313
23.03 26.17 23.90
27.47 -_ ‘5 .60 23.50
0.09 0.07 0.05
1.86 1.82 1.75
1.466 2.440 1.411
2.46-I 2.440 1.410
7.29s
323
22.04
21.75
0.03
1.68
2.394
2.395
2.290
21’P
(ps)
0.
v W)
(co)obs
ko)~lc
EC0
2.319 2.793
ac3) The nctivntion cnthnlpy (tifg in kJ mol-‘) was 3.9 2 1.2 and 4.1 2 I.2 for 3PP and ZPP, rcspccti$%?ly. It V.X calcuhrcd cording to Ilgring‘s equation 1191,shown in fig: 3. b) rp~p is the rclns~rion time chxhtcd by mcctns of rho Chum-Powlcs relationship [ 191 7&p = [ (~EIJ+ EW.)/~EOITO~~
375
I3 July 1984
CHEhlICAL PHYSICS LISTTI:RS
Volw:w 108, nunlbcr 4
-logTZ
8.2c
8.15
8.1C
3.10
3.20
3.30
3.40 +Ox
l‘llc dielectric KlilSiltioIl xcordin~ to the equation:
tiines
(7) wcrc calculated
. 1 - (Y. Such ;I distribution of rclasution times in these ~noleculcs could be due to tltc overlapping oi’ two or I~WC bands. Howcvcr, regarding the interpretation of the nwchanisn~ of the diclcctric relaxation process in tl~csc molecules. out can say tllat , 35 in previous sitnilar situations. it is quite difficult IO justify the
where
p =
prcscnce
376
of nwc
than IWO
absorption bands 3s cm-
poncn~s of rhc cornplcs band observed csperimcntally. In rhcory, tltcsc two overIapping absorptions may bc due to: (i) 111e two co~npo~~n~s (along the mutually pcrpcndicular n~olccular rotation axes) of the molecular clcctric dipole moment. assuming the molecule IO be ripid: or (ii) a fast intercovcrsion between IWO rotamers srabilised the 7; colljugation. which nx~y give rise to the appcarancc of an additional mechanism _ In both molccuics invcstigatzd. there exist two colllpollenls of the electric dipole moment. One of tllc Conq~oncnts is parallcl to the longest axis of tllc I~~OlCcUlC(SW fig.
4) and the other is perpendicular
to it. If we assunie tile presence of rigid configurations, WC can obtain 1I (tbc nlonlent of inertia connected with rotation around tiles and?* axes) and II (the moment of inertia connected with the s and z axes)
I, = $(f_\-+I:).
+I,*),
References [ 11 J. Coulon.
G. Roussy.
51. ilollcckcr.
31.X1.Claudon.
G.W. Chsntry aud E-4. Nicol, Mol. Ph\*s. 33 (1977)
377. D. Gnnct. 31. Evans and G.J. Davies. 5101. PI1ys. 30 (1971) 973. A. &do, E. Fischrr and S. hljyamoto. Phys. 2. 30 (1939) 377. J. Goulon and J.K. Rivail. Spcc~roscopir Conscquenws of Very Fast Ch~niical Processes. in: Protons and ions involved in fast dynamic Phenomena. cd. P. Laszlo (I%xicr. Amsterdxll. 197s). D.D. I&p. D.Ii. IhnbuhcI and N’.E. Vauphn. J. Chem. Phys. 50 (1969) 3904. C. N’iIIi~ms 2nd Xl. Cook. Trxns. lirx!xy Sot. 67 (1971) J. Coulon,
by using rhe relations I, = :&.
I3 July 1984
CHIShlICAL PHYSICS LETTERS
Volume 1 OS. nunibcr 4
(3)
\vlwrc lx, lJ. and I_ arc the nionwnts of inertia for the rotation around the adds. _Vand z. On this basis, one cm cspcct tile existence of two different dielectric relaxation times 7I and 7-)_ From the calculation of the rnonxnt of inertia. OIL ~911 easily obtain the ratio of the relaxation times:
990. 7I/72 which
= (/t//#) appears
= 1 .x
.
to bc the same
(4) for botll
isomers
csnmin-
cd. Tllis is the tltcorcricxl ratio calculated frotn the asswnption that thcsc niolcculcs arc rigid. Front the above value and tile values of the sanx ratio reported previously [I 0.1 1 ] _it could be suggested that. in this case. tlx diffcrcnce between the relaxathe espcdtion times 71 and 7, is too small to induce 1nc111aI1y observed distribution. TAGn~ into consideration the decrease
C. Bror,
\lolcculsr
moliuns
in liquids.
cd. J. Lascomb
(Rcidcl. Dordrccht. 1974). 1’. Frcundliclr. E. Jakuwk. IIA. KoYodTicj. A. KoII. 51. P;?jdowska and S. Sorriso. J. P!rys. Ciwm. 57 (1963) 103-l. A. Koll. I1.A. Kohdzicj and S. Sorho_ 2. Physik. Chcm. XI-. 134 (1963) 163. E. Jakusck. P. Frcundlich. 14.X. Kohdzicj and S. Sorriso. ChClll. Phys. Sl (19S3) 153. E. Jakusck. P. I~rcundlirl~. 1i.X. IiurCldi?icj. A. Koll md
Sorriso. Clicm. 1%)‘~.64 (196-l) 141. G. Xlarconi. G. Orlandi and G. Poypi. J. Photochcm. S.
tive dipole nionient with an increase in tentperature and a fidir activation cntimlpy (table 2). one could say that there is probably a fast intcrcoversion. In conclusion, these results exclude the presence of a sitnple mechanism for the dielectric relaxation process of both isonxrs. However. they are unable to distinguish between the possibilities (i) and (ii). T’his aspect is bcin, 0 studied furhtcr in our laboratory.
19 (19SZ) 329. E. Fisher, J. Photochcm. 17 (1961) 331. G. Orhndi. G. Posei 2nd G. Marconi. J. Chem. Sot. Farad;ly I1 17 (19SO) 59s. F. Xlasctti. G. Bartocci and U. 1lszzuc;lto. CZIZZ. Chim. 1131. I12 (19SZ) 255. G. Bartocci. 1:. Masctti. U. JIaz~uc~to. S. Dclloutc and G. Orhndi. Spcctrochim. Acra 36A (1961) 729. G. Bxtwxi and U. M~zzuuro. J. Lumincsccncc 27 (1962) 163. [ 161 H.A. Eutodzicj. 11. Pajdo\vska and L. Sobczyk. J. Phys.
Acknowledgeement
E. I1 (1970 752. [ 191 N.E. ltill. W.E. V;tuplxm. A.15 Price and 11. hvics. Diclcctric propcrtics and molccuhr bclraviour <\‘nn Nnstmnd, Princeton. 1969).
of tlw tffec-
WC tltank Dr. E. Jakusck for valuable discussions. Grateful acknowledgement is also nladc to the Polish Academy of Sciences and to the Consiglio Nazionalc dellc Rccrchc (Rome) for financi;ll support.
377