Gas chromatographic retention characteristics of low molecular weight methylpolysioloxanes. Part II: Structural identification of polycyclic methylpolysiloxanes based on retention

Gas Chromatographic Retention Characteristics of Low Molecular Weight Methylpolysiloxanes. Part I1: Structural Identification of Polycyclic Methylpolysiloxanes Based on Retention Index Additivity

G. A lexander / G. Garz6

Hungarian Academy of Sciences, Central Research Institute for Chemistry, Laboratory for Inorganic Chemistry, 1088 Budapest, Muzeum krt. 6-8, Hungary

Summary From retention indices of fifteen polycyclic methylpolysiloxanes the selection o f the proper structures for each of these compounds has been attempted. The fifteen substances were structural and geometric (cis-trans) isomers o f compounds of five different elementar compositions. The retention indices were considered as the sums of increments representing the characteristic atomic groups, further the structural characteristics of the molecules. Calculated structural increment - I SI - values turned out to be nearly identical for certain groups of the investigated molecules. Using a phase dependent increment for one of the characteristic atomic groups, the grouping of the measuring points was similar on all o f the stationary phases involved. This fact, and some principles derived from the structural characteristics of the polycyclic methylpolysiloxanes formed the basis for the proposed structural identifications.

I n t r o d u c t i o n

The gas chromatographic study of organic compounds of known composition and structure has revealed several correlations between gas chromatographic retention and molecular structure [1,2, 3, 4, 5].

In this paper we wish to present the selection of the proper structures for certain compounds of known compositions

but unknown structures, using a collection of retention data.

The investigated compounds have been polycyclic methylpolysiloxanes with the general symbol: TaDb ; where T represents CH3SIO3/2 and D represents (CHa)2 SiO. These compounds have been formed during the thermal degra- dation of irregular branched chain methylsiloxane poly- mers with an approximate molecular weight of 10000 [6].

Fifteen low molecular weight polycycles have been investigated. They have represented structural and geometric (cis-trans) isomers of the compounds listed in Table I. Fig. 1 demonstrates the 23 possible isomers derived from these five compositions. Our intention has been to find the proper structure for each of the fifteen preparations.

Retention data of the polycyclic methylpolysiloxanes using four different stationary phases (Apiezon L, SE-30, QF-1, Tween-60) at two different temperatures have been shown in a previous paper [7]. A special retention index has been introduced in that paper for low molecular weight methylpolysiloxanes, called the Di- methylsilo• Number: DN, referring to a scale based on the homologous series of dimethyl cyclopolysiloxanes

(Din):

_ ( l o g t~: - l o g t~3 m ) DN x -klog77- . . . . . , + m I00 (1)

tDm + 1 -- log tDm

' t' t' where tx , D m, Dm+l are the adjusted retention times

of the sample and of two subsequent cyclic dimethyl- siloxanes.

'<~>'

1 _2

3 ~ 5 6

r ~ rTl>

�9 Lz

17 18

23

2 LO

15 L6

<3"-4>:4 11 12

19 20 21 22

2~ 25 2__6

Fig. 1

Symbolic representation of the geometric isomers of the investigated polycyclic methylpolysiloxanes . . . . D unit - �9 - = T unit.

I The existence of the structures in parentheses has to be excluded, as proven by the sterie difficulties in building these molecules from space filling atom calotte models. The structures with asterisks can be modelled in two (cis and trans) configurations.

190 Chromatographia, Vol. 7, No. 4, April 1974 Originals

Table I

Compound I No. of investigated Symbol isomeric samples

Octamethyl-bicyclo- pentasiloxane T2 D3 2

Decamethyl-bicyclo- hexasiloxane T2 D4 3

Dodecamethyl-bicyclo- heptasiloxane T2 D5 3

Octamethyl-tricyclo- T4D 2 3 hexasiloxane

Decamr heptasiloxane T4D3 4

In Table 11 retent ion data expressed as the DN number are part ly the same as those described in the previous communication but given together wi th retent ion data on squalane liquid phase and the melting points o f several

samples. A new preparat ion A is also included.

In the present paper correlations between the measured DN values and the molecular structure are based on the additivity principle. This means, that DN values are considered as the sums o f increments, which are characteristic for certain atomic groups and structural elements

of the molecule.

The Addi t iv i ty o f DN Values for Methylsiloxane Polycycles

The addit ivity principle has been proved by several authors for various types o f compounds. Retent ion indices were calculated with fairly good approximat ion by addit ion of the increments which are characteristic for the skeletal atomic groups and for the functional groups of the molecules [ 5 , 8 - 1 3 ] .

Homing [ 12], Haken [ 14], Evans [3] and Schomburg [5, 13] have pointed to the fact, that certain structural and steric characteristics o f the molecules can also act as functional groups, representing a sort of retention increments, characteristic for the molecular shape and

size.

The retention index o f cyclopentane serves as an example; it equals 578 on squalane at 120 ~ Therefore 578 - 500 = 78 represents the "structural increment" for the cycling.

In the case o f polycycl ic methylpolysi loxanes CH 3 Si03/2 (T) and (CHa~h SiO (D) can be regarded as skeletal elements, and their contr ibut ion to the DN value will be designated as ITI and IDI respectively. Regarding, however the fact that DN values o f the isomeric molecules are different, it follows that here also the existence o f some kind o f "structural DN increment" - I S I - has to be encountered with.

Consequently the retent ion index o f polycyclic methylpolysiloxanes can be formulated as

fTaDblp = a [TL + b [DI + ISip (2)

where the index p indicates to the stat ionary phase.

It was pointed out in an earlier paper from this laboratory [7] that DN values for the investigated compounds were

nearly independent o f the temperature. Thus Eq. 2 holds wi thout the restriction of the constancy o f temperature.

In Eq. 2 the [TaD b Ip values are measured data; a and b follow from the composit ion o f the substances under investigation. The value of I DI is taken as 100 (Eq. 1), independent ly o f the nature o f the stat ionary phase. A first approximative est imation o f the value of ITI can

be carried out as follows:

There exists a formal stoichiometric relationship between

M = (CH3)3 SiOu2 D = (CH3)2 SiO

and

T = CH3SIO3/2 :

-CH3 + 0112 --CH3 + 01/2 M ~D >T

On this basis

L M t - [ D I = IDt -IT[ (3)

may be assumed for the DN values.

Table 11. Retention data (DN) of polycyclic methylpolysiloxanes

Sam,le I SymbolL Me'ting L S'ua ne[ APiCZ~ I t Twcon60 point ~ 110 ~ 125 ~ 95 ~ 125 ~

lx T2D 3 115 477.4 481.4 462.3 513.8 la T2D3 16.7 495.4 500.0 486.0 543.4

2a T2D4 54.5 543.4 541.9 537.2 558.6 3b T2D4 44.0 565.1 564.1 553.2 586.7 3c T2D4 2.2 573.5 576.4 567.4 606.5

ly T4D2 119 520.8 516.9 508.3 567.3 2c T4D 2 35.3 547.5 551.8 539.8 609.6 A Ta, D 2 506.0 - - -

4a T4D3 49.0 595.1 593.0 587.5 625.5 4c T4D 3 - 606.3 603.7 596.8 642.1 4d T4D 3 148 618.4 616.8 604.6 652.9 4c T4D3 - 627.4 625.3 619.7 670.0

5a2 T2D5 - 627.4 624.9 623.0 652.2 5al T2 Ds - 644.3 639.4 637.5 655.8 5b T2D s - 665.1 658.8 657.3 692.0

Chromatographia, Vol. 7, No. 4, April 1974 Originals 191

As reported in the earlier paper [7], the value o f I MI was determined and found to be 125, independent o f the nature o f the stat ionary phase and the temperature.

Thus as a first approximat ion, again independent o f the stat ionary phase

I M I - I D I = I D I - I T I =25

and

ITI = 75 (4)

ITaDb Ip = 75a + 100b + ISIp (5)

may be writ ten.

F rom Eq. 5 values o f I S I p were calculated for all polycycles. They are presented in Table III and par t ly illustrated in Figs. 2, 3 and 4.

Both axes in the figures represent DN values. The sum of the atomic increments are measured on the abscissa, while the structural increments are presented on the ordinate. It is evident that for isomers the sum o f the atomic increments is identical (75a + 100b), but I SI values show characteristic differences.

An immediate observation following from Figs. 2, 3 and 4 is, that on the basis of nearly identical I S I values the investigated fifteen polycycles form six groups.

This s ta tement holds true for the three stat ionary phases squalane, APL and QF-1 ; however, for Tween-60 the existence of certain compound groups with identical I SI value seems not to be valid.

Assuming that the phenomenon of the common k~l levels for certain compounds on the three stat ionary phases is caused by some common characteristics o f the molecules located on an I SI value level (the similar bond system, structural configuration and/or conformation o f these compounds) , the pat tern of the diagrams should be independent on the nature o f the stat ionary phase similar to those in Figs. 2, 3 and 4.

/SI

60-

50-

,~0-

30-

20"

10"

0-

- 10-

-20-

-30-

DN)

la'r" "f- 2c

lx 4- 3c t +~

3b-l-

A-~

2au

4-4e

+5b

"I-4c

-I- &a + 5q

I I I I I ~50 500 550 600 650

:reo~: :~ O~: :SD, ) :r, o3) :r2Ds)

[75a* 100b] (DN) Fig. 2

Relationship between structural increments and summarized atomic increments on squatane liquid phase.

As far the I TI values were taken 75 for all the stat ionary phases. However, variations on different stat ionary phases have to be considered as well.

Based on these assumptions, let us consider two substances (1 and 2) located on the same ISI level in Figs. 2, 3 and 4. Then we may write that

o r

ISIl ,p = ISI2,p

tTatDbl I - - a l ITlp - b l IDI = ITa2Dbz I - az ITtp - b 2 IDI (6)

Table III. Calculated t Slp values for polycyclic methylpolysiloxanes

S m0,e s, bo, lsqua,anerA,,ezo. LrOFi 1 a T 2 D 3 45.4 50.0 36.0 Ix T2Da 27.4 31.4 12.3

2c T4D2 47.5 51.8 39.8 ly T4D2 20.8 16.9 8.3 A T4D2 6.0 - -

3c T2D4 23.5 26.4 17.4 3b T2D4 15.1 14.1 3.2 2a T2D 4 - 6.6 - 8.1 - 12.8

4e T4D 3 27.4 25.4 19.7 4d T4D3 18.3 16.8 4.6 4c TaD3 6.3 3.7 - 3.2 4a T4D 3 -4 .9 - 7.0 - 12.5

5b T2Ds 15.1 8.8 7.3 5al T2Ds -5 .7 - 10.6 - 12.5 5a 2 T2D s - 22.6 - 25.1 - 27.0

Tween-60 Tween-60 T=75 T=83

93.4 77.4 63.8 47.8

109.6 77.5 67.3 37.3

56.5 40.5 36.7 20.7

8.6 - 7.4

70.0 38.0 52.9 20.9 42.1 10.1 26.5 - 5.5

42.0 26.0 5.8 - 10.2 2.2 - 13.8


151 DN IS l DN

50

20

-20

la ~" + 2c

+ 3c lx i- + 4e

+ ly 304- + 4d

2 a +

-I-4c

+ 4a

-I- Sb

-'t-5o I

~- Sa e

I I I I I 450 500 550 500 550

rr 2 D 3 ) (T~ D e) rT e D~) r~ D3) (T2D 5 )

[750 § 100b] (DN)

Fig. 3

Relationship between structural increments and summarized atomic increments on Apiezon L liquid phase.

80

70,

5 0

50,

40,

30-

20-

10-

0-

-70"

-20"

la + t 2c

l x+ 3c

7.),+ + jr4 e

3b+ "t" 4d

F4c

-t-5b

2a + + 4 a

-I'- 5at t-5a 2

I , I , I I I , I , ~50 500 550 6oo 650

<T203) ( T 4 D 2 ) (T204 ) (T~D3.) CT2D 5)

Fig. 5 f83a + lOObl (DN)

Relationship between structural increments (calculated from phase-dependent I T[p value) and summarized atomic increments on Tween-60 liquid phase.

5O

40

30

20.

10.

O

-10.

-20

-30

ISI DN

-k 2c la -l-

lx +

.I-4e 3c-I-

"1- 7y + 5b 364- -l- z d

.p 4c

2a--t - - ~ a b 5al

f- 5a 2

I I I I I 450 500 550 600 650

<TED3) <T~ D e) <TED,;) (T: D 3 ) (T2D s )

Fig. 4 [75a§ lOObJ (DN)

Relationship between structural increments and summarized atomic increments on QF-1 liquid phase.

%D3 ~D2 GD~ ~Ds ~D5

lo,,! 2c,.~

. . . . . , e

I ix ; 2 r 3 C;rS_ ,

t I

FT-I---FTI>--T-1-'> I I I

i I ' I

A;15 I - - f I I I I

2a;6_ 4a~ 1 9 5 q ; L l I

Fig. 6 ~ _ Result o f the structural ident i f icat ions ,


Expressing ITI and substituting again 100 for IDlwe get:

]TazDb2 I p - I Tal Dbt I p - 100 (b2 - b 1 ) I Tlp = a2 - a, (7)

From Eq. 7, I TITw values for five compound pairs situated each on common ISI levels in Figs. 2, 3 and 4 were calculated. Results of these calculations are shown in Table IV.

Table IV. Calculated IT ITW values

Compounds on common Isl level IT~r w (Figs. 2-4)

la -2c 83.1 3c-4e 81.6 3b-4d 83.1 4d-5b 80.5 2a-4a 83.4 4e -5al 85.3

Average 82.8

It is evident from the data in Table IV that this calculation results in IT Ip values which differ from 75, but may be regarded as constants for the given stationary phase.

Using a I T I value of 83 instead of 75 in Eq. 2, new I S I values are obtained for the phase Tween 60. In the diagram of Fig. 5 these new figures (given in the last column of Table Ili) were used. Now nearly the same pattern is seen as in Figs. 2, 3 and 4.

Similar calculations were made with data obtained on SE-30 and PEG-succinate phases. The constancy of the new I T I values was again satisfactory and the relationship between the new I SI values and the summarized atomic increments proved to be similar to those in Figs. 2 -5 .

Regarding these results, it may be concluded that the phenomenon of the common I St levels is valid for the same compound groups on all phases and the sequence of the I SI levels is also identical in the diagrams. To obtain this result, only the assumption of phase-dependent I TI values was introduced, while the I DI = 100 assumption was maintained.

Principles of the Structural Identification

In our earlier paper [7] it was proved in details, that linear siloxane compounds (M2 Dn) and cyclic siloxanes (Dn) could be regarded as homologous series also in a "gas chromatographic sense". This meant that the addi- tion of one D atomic group to any of these compounds always resulted in a retention increment of 100 DN units.

In the case of polycyclic methylpolysiloxanes, however, certain restrictions are necessary with regards to the concept of homology, because of the existence of several, structural and cis-trans isomeric configurations.

Figs. 2 - 5 may provide a basis for the definition of the so-called "structural homology":

Polycydic methylpolysiloxanes with stoichiometric formulae differing in one D atomic group and having

DN values which differ approximately by 100 units will be designated in the following as "structural homologues'" The corresponding compounds have evidently nearly identical I S[ values, i.e. they are situated on common I S I levels in Figs. 2 - 5 .

Consequently the structural homologues in Figs. 2 - 5 are: Ix and 3c, ly and 4e, 3b and 5b, 2a and 5a~.

Based again on Figs. 2 -5 , we further introduce the designation "structural analogy" for molecule pairs, like

la and 2c, 3c and 4e, etc.

In other words those molecules are designated as structural analogues which have nearly identical I SI values and stoichiometrically are not homologous.

In order to draw conclusions for the molecular structures from Figs. 2 - 5 , some interpretations are needed to explain the common pattern in these figures, i. e. to decide, which structure is expected to have a high or a low I SI value within one isomer group, and - on the other hand - what kind of characteristics do force some structures to common I St levels.

In the following assumptions - which form the basis of the interpretations - mainly the experiences gained with space-filling atom calotte models of all the polycycles were taken into account [6].

1. Structural homology and analogy (common 1SI levels) definitely mean similar intermolecular forces, i. e. similar degrees of solvation (interactions between solute molecules and the stationary phase). For such molecules a similar shape of the molecule is also assumed.

If the covalent bond system of the molecule is flexible, the molecular shape is governed by a well-known general tendency of the siloxanes. According to this, if not hinder- ed, these molecules tend to form intramolecular quadru- poles from pairs -- Si ~ + - O ~ - - atomic dipoles. This leads to the formation of stable conformers, which are not destroyed even in the environment of polar stationary phases [17].

In non-flexible, rigid molecules, molecular shapes are determined by the bond system.

2. Figs. 2 - 5 indicate that the same compound groups are situated on the common I S I levels on both apolar and polar phases, and the sequence of the I S I levels is also identical on both squalane and Tween-60. It follows that the retention of the polycyclic methylpolysiloxanes is mainly directed by dispersion (London) forces.

The strength of the dispersion forces is inversely pro- portional to the sixth power of the distance, therefore only the atomic groups situated on the "molecular surface" contribute to the intermolecular interactions.

Therefore we assume that high I S I values, which mean considerable solvation, are caused by a relatively great number of unshielded atoms on the molecular surface. On the other hand, it is evident using space filling atom culotte models that the number of the unshielded atoms on the molecular surface is closely related to the symmetry of the T and D group arrangements in the molecule.


As an example we present an estimation of the number of unshielded atoms on the "molecular surface" for two different isomeric molecular structures.

Regarding two T4D2 samples (structures 13 cis and 15), it is clear from the schematic structures in Fig. 1, that the symmetry of the T - D arrangement is higher in the latter structure.

From the examination of the atomic calotte models it turned out, that the areas covering the siloxane skeleton of these two structures were approximately equal. Con- siderable differences were found at the same time, regarding the distribution of the CH3 groups on the surfaces.

In case of structure 15, a fully uniform distribution was observed. The surface areas on the siloxane skeleton, belonging to each CH 3 group were equal (approximately 16 arbitrary area units), thus permitting free rotation, and a maximum shielding effect of the CH3 groups towards the siloxane skeleton.

However, in case of structure 13 cis, CH 3 groups were accumulating in 20 % of the area covering the siloxane skeleton (one CH3 group on approximately 6 area units of the surface), while 80 % of the surface was only poorly shielded (one CH3 group on approximately 26 area units).

Similar relationships were also observed in the case of other molecular models: asymmetric situation of the T and D atomic groups always resulted in considerably "bare" siloxane surfaces. Therefore, in our structural identifications an asymmetric situation of the T and D atomic groups is assumed to cause high I SI values, while low I SI values are regarded to indicate the symmetry of the T - D arrangement. We further assume that the stabil conformers of the flexible structures represent a high degree of T - D symmetry, and this results in low ISI values for these molecules.

The above assumptions are also supported by Sakharov

[18]. According to his results, the closer the mutually repulsed groups are spaced, the greater is the increase in the retention parameters of a particular molecule. An accumulation of the methyl groups serves as an example.

Structural Identification

Based on the previous discussion, we present here the speculations which led to the correlations between retention and structure, as summarized in Fig. 6. The retentions corresponding to the structures in Fig. 6 are listed in Table II.

1. 29Si-NMR measurements were performed with materials la and 3b. It was found [15, 16]:

T2D3 la = structure 1 *) (8)

and

T2 D4 3b = structure 4 (9)

2. There are two consequences of the above identifications:

T2Da lx = structure 2 (10)

*) These numbers refer to the serial numbers of the structures in Fig. 1.

and

T4D2 2c = structure 13 (11)

The first statement follows from Fig. 1, where the existence of not more than two structures for T2D3 is documented. The latter statement is based on the analogy of la and 2c (see Figs. 2 -6) . Regarding namely the three possible structures for T4D2 in Fig. 1, clearly only 13 shows an analogous shape and T - D symmetry to 1.

As proved by atomic calotte models of these molecules, structures 1 and 13 are comparatively nonflexible due to the stiffening effect of the fused trisiloxane cycle(s). Asymmetric situation of T and D groups in these structures follows from the steric arrangement of the bond system. In 1 the plains of the two rings are nearly perpendicular. In the case of sample 2c, the cis orientation of structure 13 is proposed.

3. T2D3 lx and T2D4 3c are structural homologues, as seen in Figs. 2 -6 . Thus regarding Fig. 1, only


is possible, if similar molecular shape and T - D symmetry to structure 2 is required.

4. The position of T4D2 ly is somewhat uncertain between two I Sl levels in Figs. 2 - 5 . Nevertheless, it is clear that it has a medium I S I value between those of the isomeric samples 2c and A. It follows from Fig. 1, that out of the remaining structural variants 15 and 16 (Eq. 11), structure 16 should be preferred for ly, because here the D groups are more asymmetrically situated than in structure 15. Therefore we may write:

T4D2 ly = structure 16 (13)

5. From Eq. 9 it follows that

T4D3 4d = structure 17 (14)

and

T2Ds 5b = structure 8 (15)

Namely the relation between 3b and 5b is homology, and between 3b and 4d analogy (Figs. 2 -6 ) . The only choice for analogue structure to 4 is 17, and for homologue structure: 8, in Fig. 1.

6. If we now consider that for T2 D4 2a only structures 3 and 6 have remained and on the other hand, 2a is characterized by a rather low I SI value, we have to select for 2a the structure with a higher symmetry concerning the position of the T and D groups. Thus we may write:

T2D4 2a = structure 6 (16)

Structure 6 is rather flexible. Therefore the molecular shape is directed by the formation of siloxane quadru- poles thus leading to a conformation with decreased number of atoms on the molecular surface.'This is the reason for the low solvation interactions with the stationary phase, manifested by relatively low I SI values.


7. Equation 16 and the homology between samples 2a and 5a~ give grounds for declaring that

T2 Ds 5al = structure 11 (17)

(see Fig. 1 and 8).

8. T2Ds 5az shows the lowest ISI value among all the samples investigated. In accordance with the requirement o f a highly flexible bond system with effective intramolecular forces counteracting the intermolecular forces:

T2Ds 5a2 = structure 12 (18)

has to be declared.

9. Considering that we have accepted structure 17 for sample 4d, the structure for 4a has to be more symmetric concerning T - D arrangement and/or more flexible than 17. Further the analogy with samples 2a and 5al has to be considered.

Tetrahedrical structures 2 2 - 2 6 are neither flexible nor symmetric, as proved by the atom calotte models.

From the remaining structures 18 and 19:

T4D3 4a = structure 19 (19)

seems to be the better choice. The reason for this is visualized in Fig. 7A. Here a schematic illustration o f a rather probable conformation for 5al is given. The analogy of the steric arrangements o f structures I 1 and 19 is verified this way.

10. In Fig. 7B we wish to prove that structure 18 at the same time has to be regarded as analogous to 5a: = 12, consequently it is excluded as a structure for 4e and 4c. The tetrahedral structures 2 2 - 2 6 remain for the latter samples. The structural variant o f the highest symmetry conceming T and D groups among these structures is 24. The choice:


is therefore in accordance with the lower I SI value o f this sample compared to 4e.

11. For T4D2 isomers there are three possible structures and two of them (2c and ly ) have been identified earlier, thus only one structure remains for sample A. Therefore:

T4D2 A = structure 15 (21)

Eq. 21 is further supported by the fact that while A has the lowest IS I-value among the T4 D2 isomers, 15 has the highest T - D symmetry among the T4D2 structures.

The probability o f Eq. 20 is even higher considering Eq. 21 because of the homology between 4c and A and the close similarity of structures 24 and 15.

12. For the remaining sample 4e structures 22, 23, 25 and 26 have remained. Our informations do not allow further restrictions concerning the structure o f sample 4e.

As a conclusion we wish to emphasize the hypothetical nature of the structural identifications. They are to be proved by direct methods, presumably NMR spectroscopy.

A

Ca

Fig. 7

B

5~ X

Schematic illustrations of the suggested conformations for structures 11 and 12.

By now our considerations serve mainly as examples for the possibifities in the structural identification based on gas chromatographic retention data.

Since polycyclic methylpolysiloxanes have not been characterized in the literature until now, our data serve at the same time as a gas chromatographic characterization o f these compounds.

Acknowledgement We are deeply indebted to Dr. H. Jancke (Central Research Institute for Physical Chemistry of the German Academy of Sciences, Berlin GDR), who has performed the 29Si-NMR measurements, in a laboratory of the Academy of Sciences of the Estonian SSR (USSR).

References

[ 11 E. Kovdts, in Advances in Chromatography (J. C. Giddings, R. A. Keller, Eds.), Vol. 1. M. Dekker, New York 1965 ; pp. 229-247.

12] Ir J. A. Fan den HeuveL E. C Homing, Biochim. Biophys. Acta 64, 416 (1962).

131 M.B. Evans, Chromatographia 2, 397 (1969). I41 J.J. Walraven, A. W. Ladon, in Gas Chromatography 19713

(R. Stock, S. G. Perry, Eds.), Institute of Petroleum, London 1971, pp. 344-380.

[51 G. Schomburg, Advances in Chromatography (J. C. Giddings R. A. Keller, Eds.), Vol. 6, M. Dekker, New York 1965; pp. 211-245.

161 G. Garz6, J. Tamds, T. Sz~kely, K. U#zdszi, Acta Chim. Acad. Sci. Hung. 69, 273 (1971).

[71 G. Garzd, G. Alexander, Chromatographia 4, 554 (1971). [81 G. Z Pierotti et al., J. Am. Chem. Soc. 78, 2989 (1956). 191 M.B. Evans, J. F. Smith, Nature 190, 905 (1961).

Ii01 M.B. Evans, J. F. Smith, J. Chromatog. 8, 303 (1962). I1 i I P.A .T . Swoboda, Gas Chromatography 1962 (M. van

Swaay, Ed.), Buttcrworth, 1962; pp. 273-291. [ 121 E.C. Homing, W. J.A. Van den Heuvel, Advances in

Chromatography (J. C. Giddings, R. A. Keller, Eds.), Vol. 1, M. Dekker, New York 1965; pp. 153-198.

[131 G. Schomburg, Chromatographia 4, 286 (1971). 114] J.K. Haken, J. Chromatog. 23,375 (1966). 1151 G. Engelhardt, H. Jancke, J. Organometal. Chem. 28,

293 (1971). [161 H. Jancke, G. Engelhardt, M. Mi~gL E. Lippmaa, Z. Chem.

13,392 (1973). 1171 W. Noll et al., Ber. der Bunsenges. 67, 407 (1963). 1181 V.M. Sakharov, J. Chromatog. 65, 103 (1972).

Received: Oct. 1, 1973 Accepted: Jan. 2, 1974


Documents

Gas chromatographic retention characteristics of low molecular weight methylpolysioloxanes. Part II: Structural identification of polycyclic methylpolysiloxanes based on retention