`
`
`
`
`
`Liquid-Phase Hydrogen Bonding and Raman
`Spectrometry
`II—Primary and Secondary Amines
`
`
`
`
`
`C. Perchard and J. P. Perchard
`Molecular Spectrochemistry Laboratory, Pierre and Marie Curie University, 10 Rue Cuvier 75230 Paris Cedex 05, France
`
`Structure, intensity and depolarization ratio of NH or NH2 Raman bands of some primary and secondary amines
`have been studied in pure liquid state at different temperatures and in dilute CCl4 solutions. The depolarization
`ratio and scattering activity, as in the case of alcohols previously studied, increase with self-association. It confirms
`the change of the XH bond polarizability derivatives with hydrogen bond formation.
`
`
`
`
`INTRODUCTION
`
`As part of a study of weak hydrogen bonds by Raman
`spectrometry, we present here results obtained on the
`NH···N system relating to simple primary or secondary
`amines. In previous work1 on the νOH band of the O‒
`H···O liquid alcohol system, two noteworthy results were
`obtained: a two-compound structure due to the molecules’
`chain association, and a significant increase in the
`scattering activity (45α’2 + 7γ’2) and in the depolarization
`ratio through self-association.
`Our study is divided into two parts, the first of which
`relates to a description of the liquid-phase vNH or vNH2
`bands from the triple point to the vicinity of the critical
`point, and the second to intensity measurements on those
`same bands.
`The primary amines studied are methylamine and
`ethylamine;
`the secondary amines, dimethylamine,
`diethylamine (and the corresponding ND-deuterated
`species) and pyrrole.
`
`EXPERIMENTAL PART
`
`The hydrogenated species come from Rhône-Poulenc.
`The compounds are introduced by vacuum distillation
`into the measuring cell. The deuterated species were
`prepared through successive exchanges of hydrochloride
`in heavy water. The
`isotopic
`rate, controlled
`spectroscopically, is over 90%.
`The spectra recording technique has been described
`previously.1 All amines are perfectly stable in the laser
`beam with the exception of the pyrrole, which requires
`working at low power (50 mW) and renewing the contents
`of the cell approximately every hour.
`
`† Part I: see Ref. 1.
`
`© Heyden & Son Ltd, 1977
`
`
`
`74
`
`
`
`JOURNAL OF RAMAN SPECTROSCOPY, VOL. 6, NO. 2, 1977
`
`DESCRIPTION OF THE vNH AND vNH2 BANDS
`
`Secondary amines
`
`Dimethylamine. The change in the IVV and IVH spectra is
`presented in Fig. 1. At high temperatures, the IVV
`compound
`is symmetrical and small
`in width,
`characteristic of free NH vibrators. At a
`lower
`temperature, a second wide band appears in the shoulders
`of the previous one around the low frequencies and
`gradually replaces it as it cools; it corresponds to the
`NH···N vibrators disrupted by hydrogen bond formation.
`In the vicinity of the melting point, the monomeric band
`has almost completely disappeared, while the IVV and IVH
`compounds have maximum values of 3247 cm-1 and 3258
`cm-1 respectively. In the transition to the crystalline phase,
`the two-compound structure remains, with the respective
`maximum values of 3215 and 3238 cm-1 at 170 K. These
`results may be interpreted as follows: as has already been
`observed in infrared,2 the degree of self-association is
`much lower for amines than for alcohols of an equivalent
`formula. The monomeric band (or potentially chain end)
`is observed at a much
`lower
`temperature
`for
`dimethylamine than for isoproprylic alcohol and only
`disappears at about 190 K instead of 360 K for alcohol.
`The discrepancy between IVV and IVH observed then for
`the self-associated band may be interpreted, as in the case
`of alcohol, by a coupling effect between NH vibrators; as
`the interaction between NH vibrators is weaker than it is
`between OH vibrators, the rupture observed here is much
`smaller and only really appears in the vicinity of the
`melting point. The continuity observed in the bands’
`structure in the transition to the crystalline state is
`evidence of a short-range order in liquid phase. Because
`of the absence of crystallographic data, we cannot specify
`whether this is a chain association or not.
`Similar measurements were made on the deuterated
`species (CH3)2ND, but analysis of the results was
`complicated by a Fermi resonance between the vND
`vibration and a combination around 2500 cm-1 observed
`in Bothe the liquid phase and in the gaseous state.3 The
`change in liquid spectra is shown in Fig. 2; at high
`temperature, as in the gaseous state, the high-frequency
`
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`LIQUID-PHASE HYDROGEN BOND AND RAMAN SPECTROMETRY
`
`IVV
`
`416 K
`
`IVV
`
`IVH 272 K
`
`IVV
`
`IVH 180 K
`
`Crystal
`
`177 K
`
`an NH/ND isotopic dilution effect at the same
`temperature indicates a shift towards high frequencies
`(3216 cm-1).
`For this compound, we therefore conclude that the
`effects of self-association are weak in the liquid phase, as
`the polymerization stage barely exceeds the dimer stage.
`Spectrum analysis of the corresponding ND compound
`appears more complex due to a resonance comparable to
`the one mentioned for dimethylamine. However, we find
`the main characters of
`the NH solid (Fig. 4):
`conformational
`equilibrium
`characterized
`by
`a
`duplication of the monomer band and a very pronounced
`shift of the polymer band in the transition to the
`crystalline state (2365 cm-1 2391 cm-1).
`Pyrrole. For the pyrrole, we find results already discussed
`by Lautié.5 Between 300 and 200 K, the spectra of the
`liquid or glassy compounds have wide bands, replaced in
`the crystalline state by two fine lines due to an
`intermolecular coupling effect.
`
`
`(CH3)2 ND
`
`419 K
`
`295 K
`
`182 K
`
`Crystal
`
`2500
`
`cm-1
`
`Figure 2. (CH3)2ND. Spectra IVV and IVH at different temperatures.
`The intensity of the IVH compounds has increased fivefold. Spectral
`slit width 1.7 cm-1.
`
`2300
`
`3400
`
`
`Figure 1. (CH3)2NH. Spectra IVV and IVH at different temperatures.
`The intensity of the IVH compounds has increased fivefold. Spectral
`slit width 1.5 cm-1.
`
`
`3200
`
`cm-1
`
`compound is the most intense, indicating that the
`fundamental vND largely contributes to the intensity of
`this band. Through cooling, the frequency of the
`fundamental decreases and the intensity of the high-
`frequency band gradually weakens, becoming negligible
`in the crystal spectrum at 170 K. Because of the
`complexity, it appears difficult to discuss the relative
`positions of the IVV and IVH compounds. It should be
`noted, however, that in the vicinity of the melting point,
`the IVH compound shifts to high frequencies by some 10
`cm-1 compared to the IVV compound.
`Diethylamide. The change in the spectra of the vNH
`band of the liquid diethylamine differs significantly
`from that observed for the dimethylamine. On the one
`hand, the band corresponding to the free NH vibrator
`splits at high temperatures (Fig. 3) as a result of the
`existence of rotational isomers 4: at 416 K, the two
`compounds were measured at 3340 and 3327 cm-1, the
`high-frequency band gradually weakening as the
`temperature was lowered. From this observation, we
`therefore
`conclude
`that
`the most
`stable
`thermodynamic isomer must be associated with the
`low-frequency band. Moreover, in the vicinity of the
`melting point, the free band is still large and the
`associated band appears at 3263 cm-1. On the crystal
`spectrum, only one compound strongly shifted to the
`low frequencies appears (3205 cm-1 at 220 K), while
`
`
`
`JOURNAL OF RAMAN SPECTROSCOPY, VOL. 6, NO. 2, 1977
`
`75
`
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`

`
`
`C. PERCHARD AND J. P. PERCHARD
`
`corresponding to vs widens considerably and becomes
`dissymmetrical, due to a greater sensitivity to molecule
`association. In addition, a band appears around 3180 cm-1,
`already observed by Wolff6 in absorption, and probably
`attributable to the harmonic of the vibration δ NH2 exalted
`by Fermi resonance with the vibration vs. In the crystalline
`state, four compounds appear at 3325, 3265, 3237 and 3179
`cm-1.
`for
`spectra were obtained
`Methylamine. Similar
`methylamine in both the liquid and solid states. The crystal
`spectrum was interpreted6 taking into account the existence,
`proven by a crystallographic study,7 of two types of
`hydrogen bond and a Fermi resonance at level 2δNH2.
`
`INTENSITY MEASUREMENTS OF THE vNH
`BANDS
`
`(C2H5)2 ND
`
`417 K
`
`295 K
`
`230 K
`
`Crystal
`
`223 K
`
`2500
`
`2400
`
`cm-1
`
`
`Figure 4. (C2H5)2Nd. Spectra IVV at different temperatures.
`Spectral slit width 3.3 cm-1.
`
`(C2H5)2 NH
`
`416 K
`
`295 K
`
`230 K
`
`Crystal
`
`218 K
`
`3200
`
`cm-1
`
`3400
`
`3300
`
`
`IVH at different
`IVV and
`(C2H5)2NH. Spectra
`Figure 3.
`temperatures. The intensity of the IVH compounds has been
`multiplied by 10 for the spectra at 416 and 295 K and by five for
`the spectrum at 230 K. Spectral slit width 3.0 cm -1.
`
`
`In our Raman study, we also observe that in the liquid or
`glassy state, the IVH compound has shifted by 8 cm-1 at the
`maximum around the high frequencies in comparison to
`the IVV compound (Fig. 5). As with the crystal, we
`associate
`this phenomenon with
`the existence of
`couplings between NH vibrators, associated with a short-
`range order in the so-called disordered phases.
`
`Primary amines
`
`The combination of methylamine and ethylamine and the
`structure of the corresponding vNH2 bands have already
`been discussed at length by Wolff et al.6 based on infrared
`and Raman results.
`Ethylamine. At high temperature (414 K), the two va and
`vs bands are observed respectively at around 3387 and
`3334 cm-1 (Fig. 6), and correspond to the NH2 vibrators
`not engaged in hydrogen bonding. When the temperature
`drops to 196 K, the maximums of the two bands decrease,
`respectively, by 30 cm-1 for va and 50 cm-1 for vs; the band
`
`76
`
`
`
`JOURNAL OF RAMAN SPECTROSCOPY, VOL. 6, NO. 2, 1977
`
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`

`
`
`LIQUID-PHASE HYDROGEN BOND AND RAMAN SPECTROMETRY
`
`Pyrrole
`220K
`
`C2H5 NH2
`
`IVV
`
`IVH
`
`IVV
`
`IVH
`
`3450
`
`3400
`
`
`Figure 5. Comparison of the Raman spectra (IVV and IVH) of
`pyrrole in the glassy state and the crystal state at 220 K. For the
`glassy state, the intensity of the compound IVH has increased
`fivefold. Spectral slit width 5.3 cm -1.
`
`
`3350
`
`cm-1
`
`414 K
`
`295 K
`
`196 K
`
`Crystal
`
`3500
`
`3100 cm-1
`
`Figure 6. C2H5NH2. Spectra IVV and IVH at different temperatures. The
`intensity of the IVV compounds was multiplied by 10 at 414 K, by five
`at 295 K and by 2.5 at 196 K. Spectral slit width 3.0 cm-1.
`
`3300
`
`Scattering activity measurements
`
`ρNH 0 · 20
`
`0 · 16
`
`0 · 12
`
`(CH3)2 NH
`
`Solution
`
`Gas
`
`0 · 6
`
`0 · 4
`
`(dσ / dΩ) CH3
`
`(dσ / dΩ) NH (D)
`
`200
`
`300
`
`
`Figure 7. (CH3)2NH(D). Change according to the temperature of the
`depolarization ratio ρNH of the ν(NH) band, and of the scattering
`cross-section ratio of the ν(NH) [] or ν(ND) band [] and of the
`νSCH3 BAND.
`
`
`400
`
`T (K)
`
`As we did with the alcohols, here we studied the change in
`the depolarization ratio and the intensity of the amines’ vNH
`bands according to their physical condition and, as a result,
`the state of self-association by hydrogen bond. Two types of
`measurements were carried out: on the one hand, cross-
`section and scattering activity measurements, with the
`compounds taken at ordinary temperature in the gaseous
`state, the liquid state or dissolved in CCl4, and, on the other,
`measurements of the relative intensity of the vNH bands in
`comparison to the vCH bands, according to temperature,
`with the compounds in a liquid state.
`
`Relative intensity measurements on the liquid
`
`Relative intensity measurements were carried out on the
`NH and ND dimethylamines and the NH diethylamine from
`the triple point to the vicinity of the critical point. For the
`dimethylamine, the CH band chosen for comparison was
`the low-frequency band (vsC3) located around 2780 cm-1;
`for the diethylamine, the comparison was made with the
`vCH solid as a whole between 2700 and 3000 cm-1.
`Measurements of the vNH band’s depolarization ratio were
`also carried out.
`All the results are presented in Figs. 7 and 8. It is clear in
`all cases that the ratio of the INH / ICH3 intensities increases
`significantly from the critical point (low-density liquid, with
`the molecules not self-associated) to the triple point (self-
`associated molecules); at the same time, the depolarization
`ratio of the vNH bands increases from 0.13 to 0.19.
`These results are very similar to those obtained for tert-
`Butyl alcohol.1 They suggest that, assuming the intensity of
`the vCH bands is independent from the molecules’ state of
`association, the intensity of the vNH bands increases
`through self-association.
`
`
`
`JOURNAL OF RAMAN SPECTROSCOPY, VOL. 6, NO. 2, 1977
`
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`
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`

`
`
`C. PERCHARD AND J. P. PERCHARD
`
`able to verify, on cases in which the index was known
`(e.g., ethylamine), that this method enabled us to attain
`the liquid index quite accurately.
`The intensity measurements were carried out not only
`on the vNH bands, but on the vCH bands as well, for
`comparison. In the case of the methylamine and the
`dimethylamine, the vCH bands considered were located
`around 2820 and 2,780 cm-1, respectively; except in the
`gaseous state, these bands were not perfectly insulated but
`were slightly overlapped with other, higher-frequency
`bands. To determine their surface, we made a graphic
`breakdown of the high-frequency wing, resulting in an
`error of a few percentage points. For the other amines
`(ethyl and diethylamine, pyrrole), we measured the
`intensity of the vCH solid as a whole.
`All of the results are presented in Table 1, into which
`we have carried over the depolarization ratios, the cross-
`sections and the scattering activities, as well as the cross-
`section ratios in the liquid state and the dissolved state.
`The results presented are an average of 4-6 measurements,
`half of which were carried out in the internal reference
`and half in the external reference.
`On reading this table, it appears that the intensities of
`the vCH bands vary little according to the physical state,
`while the intensities of the vNH bands change more
`significantly, except in the case of diethylamine, which in
`fact is hardly associated at 295 K. The most significant
`example is that of the pyrrole, highly self-associated in the
`liquid state, whose scattering activity increases by 50%
`through self-association. For the other amines, partially
`self-associated in the liquid state at 295 K, the increased
`intensity of NH or NH2 bands is less marked from the
`solution to the liquid. However, the general trend of the
`results seems to confirm those obtained for the alcohols,1
`namely, that the intensity of the vXH Raman bands
`increases when X‒H···X hydrogen bonds are formed.
`This variation, which is accompanied by a large
`increase in the depolarization ratio, had been associated
`′ / 𝛼𝜌
`′ ratio as a result of
`with a marked increase in the 𝛼1
`′ being the derivative of the
`hydrogen bond formation,1 𝛼1
`polarizability of the XH bond along the axis of this bond
`
`(CH3)2 NH
`
`NH 0 · 20
`ρ
`
`0 · 16
`
`0 · 12
`
`Solution
`
`0 · 09
`
`0 · 07
`
`(dσ / dΩ) C2H3
`
`(dσ / dΩ) NH
`
`200
`
`300
`
`400 T (K)
`
`
`
`Figure 8. (C2H5)2NH. Change according to the temperature of the
`depolarization ratio ρNH of the ν(NH) band, and of the scattering
`cross-section ratio of the ν(NH) band and of the ν(C2H5) solid.
`
`
`The measurements of cross-section (dσ / dΩ) and scattering
`activity (SA), already defined in reference 1, were carried
`out according to both internal and external reference
`techniques for the liquids and the solutions and according
`to the external reference technique for the gas. In the
`internal reference technique, we chose as a reference the
`band at 991 cm-1 of benzene introduced in small quantities
`into the sample and, in the external reference method, the
`same band of benzene or the v1 band of CCl4. For the gas,
`the external reference band is the v1 band of methane,
`whose intensity was determined beforehand by comparing
`it with the intensity of nitrogen.8
`The internal reference measurement technique has been
`described previously.1 The external reference technique is
`the same as the one described by Nestor and Lippincott.9
`In both cases, to make any corrections, it is necessary to
`know the index of the medium. For the dilute CCl4
`solutions, the index chosen was the one for solvents; for
`the liquid methylamine, the index was not known at the
`temperature at which the experiment was conducted (295
`K). We calculated it from the known values of the specific
`mass using the molecular refraction method.10 We were
`
`Changes in the depolarization ratio intensity of the vNH band of some amines according to physical state at 295 K
`
`
`C3NH2
`
`νNH2
`
`νsCH3
`
`C2H5NH2
`νCH
`νNH2
`
`a(CH3)2NH
`νNH
`νSCH3
`
`(C2H5)2NH
`νNH
`νCH
`
`Pyrrole
`νCH
`
`νNH
`
`1.0
`
`3.9
`
`3.0
`
`8.8
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`1.6
`
`6.5
`
`0.74
`
`2.2
`
`1.6
`
`6.3
`
`8.1
`
`25.3
`
`0.13
`
`0.03
`
`0.12
`
`0.17
`
`0.12
`
`0.25
`
`0.14
`
`0.01
`
`0.13
`
`0.17
`
`1.2
`
`4.4
`
`1.7
`
`1.0
`
`2.0
`
`7.7
`
`1 L
`
`
`
`dσ
`
` x
`dΩ
`SA
`
`
`
`Table 1.
`
`
`
`
`Gas
`
`
`
`
`1.15
`
`4.6
`
`2.2
`
`6.6
`
`1.2
`
`4.6
`
`14.7
`
`46.0
`
`5.1
`
`15.6
`
`6.7
`
`2.9
`
`8.1
`
`24.1
`
`0.15
`
`0.03
`
`0.15
`
`0.17
`
`0.20
`
`0.28
`
`0.13
`
`0.01
`
`0.16
`
`0.17
`
`1.5
`
`6.1
`
`1.3
`
`2.7
`
`7.9
`
`1.2
`
`1.3
`
`5.2
`
`16.7
`
`1.9
`
`4.5
`
`52.2
`
`7.9
`
`16.0
`
`1.1
`
`1.1
`
`1.5
`
`1.0
`
`2.4
`
`9.4
`
`1.4
`
`1.1
`
`3.1
`
`2.8
`
`9.3
`
`11.0
`
`29.2
`
`1.1
`
`1.4
`
`1.2
`
`ρ
`dσ
`
` x
`dΩ
`SA
`
`1 L
`
`
`
`ρ
`dσ
`
` x
`dΩ
`SA
`
`1 L
`
`
`
`CCI4 solution
`
`
`
`
`
`Liquid
`
`
`
`(SA) liquid / (SA) solution
`
`a L refers to the internal field factor corresponding to each medium.1 The scattering cross-sections dσ/dΩ are expressed in 10-30 cm2 mol-1 sr-1
`and the scattering activities SA in 10-7 cm-4 g-1 mol-1.
`
`78
`
`
`
`JOURNAL OF RAMAN SPECTROSCOPY, VOL. 6, NO. 2, 1977
`
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`IPR2020-00040
`
`

`

`LIQUID-PHASE HYDROGEN BOND AND RAMAN SPECTROMETRY
`
`Table 2.
`
`cross-section and depolarization ratio of some
`v(XH) bands of “free” or XH···X-hydrogen-bond-
`associated XH groups at 295 K. Corresponding
`′ and 𝜶𝝆
`variations in derived polarizabilities 𝜶𝟏
`
`
`
`
`
`
`
`
`
`
`
`a
`
`CH3OH
`CD3OH
`
`(CH3)2CHOH
`(CD3)2CHOH
`
`
`
`
`
`(CH3)3COH
`
`Pyrrole
`
`Solution
`diluted
`in CCI4
`
`
`
`
`Pure liquid
`
`
`
`SA
`ρ
`{
`′𝑠𝑜𝑙
`𝛼1
`′𝑠𝑜𝑙
`𝛼𝜌
`
`
`SA
`ρ
`{
`′𝑙𝑖𝑞
`𝛼1
`′𝑙𝑖𝑞
`𝛼𝜌
`
`
`
`
`′𝑙𝑖𝑞
`𝛼𝑖
`′𝑠𝑜𝑙
`𝛼𝑖
`′𝑙𝑖𝑞
`𝛼𝜌
`′𝑠𝑜𝑙
`𝛼𝜌
`a The scattering activities SA are expressed in 10-7cm4 g-1 mol-1 and
`the derived polarizabilities in 10-7/2 cm2 g-1/2 mol-1/2.
`
`3.3
`0.11
`0.46
`0.13
`
`
`4.7
`0.19
`0.59
`0.09
`
`4.1
`0.11
`0.51
`0.14
`
`
`7.3
`0.17
`0.72
`0.13
`
`4.4
`0.11
`0.53
`0.15
`
`
`7.3
`0.21
`0,74
`0.09
`
`5.1
`0.12
`0.58
`0.15
`
`
`7.9
`0.20
`0.77
`0.11
`
`1.28
`
`1.41
`
`1.40
`
`1.33
`
`0.69
`
`0.93
`
`0.60
`
`0.73
`
`
`
`are consistent with those obtained on the vCD band of
`deuterochloroform.11,12
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`′ perpendicular to it. By using the two experimental
`and 𝛼𝜌
`data simultaneously—the v(XH) band’s scattering activity
`SA and depolarization ratio ρ—, it is possible to
`′ and 𝛼𝜌
`′ .
`separately specify the variations in derivatives 𝛼1
`In effect,
`
`′ + 2𝛼𝜌
`′ - 𝛼𝜌
`′ )2
`′ )2 + 7(𝛼1
`SA = 5(𝛼1
`
`and
`
`2
`
`
`
`′ + 2𝛼𝜌′ )
`
`′ − 𝛼𝜌′ )
`
`′ − 𝛼𝜌
`′ )
`3(𝛼1
`ρ =
`2
`
`
`5(𝛼1
` + 4(𝛼1
`′ and 𝛼𝜌
`′ may be calculated from the sizes of
`As a result, 𝛼1
`SA and ρ:
`
`2
`
`+ 2√𝜌)
`
` (√
`
`3−4𝜌
`
`5
`
`𝑆𝐴
`
`3(𝜌+1)
`
`√
`
`1 3
`
`′ =
`𝛼1
`
`− √𝜌).
`
` (√
`
`3−4𝜌
`
`5
`
`𝑆𝐴
`
`3(𝜌+1)
`
`√
`
`1 3
`
`′ =
`𝛼1
`
`The same formulas are obtained in the case of the
`infinite, planar zigzag chain of XH bonds applicable to
`alcohols.1
`The results for the compounds, alcohols and pyrrole,
`whose variations in intensity are clear, are brought
`together in Table 2. The consequence of hydrogen bond
`formation is an elongation of the ellipsoid of the derived
`′ increasing
`polarizabilities, with the longitudinal axis 𝛼1
`′
`while the perpendicular axis 𝛼𝜌
` decreases. These results
`
`BIBLIOGRAPHY
`
`
`
`1. C. Perchard and J. P. Perchard, J. Raman Spectros. 3, 277
`
`(1975).
`2. M. Cl. Bernard-Houplain and C. Sandorfy, J. Chem. Phys. 56,
`3412 (1972).
`3. J. P. Perchard, M. T. Forel and M. L. Josien, J. Chim. Phys. 61,
`652 (1964).
`4. G. Gamer and H. Wolff, Spectrochim. Acta Part A 29, 129
`(1973); G. Gamer and H. Wolff, Spectrochim. Acta Part A 28,
`2121 (1972).
`5. A. Lautie and A Novak, Can. J. Spectrosc. 17, 113 (1972); A.
`Lautie and A. Novak, J. Chem. Phys. 56, 2479 (1972).
`6. H. Wolff and D. Staschewski, Ber. Bunsenges Phys. Chem. 68,
`135 (1964); H. Wolff and H. Ludwig, Ber. Bunsenges Phys.
`Chem. 68, 474 (1964).
`7. M. Atoji and W. N. Lipscomb, Acta Crystallogr. 5, 606 (1953).
`
`
`8. H. A. Hyatt, J. M. Cherlow, W. R. Fenner and S. P. S. Porto
`J.O.S.A. 63, 1604(1973).
`9. J. R. Nestor and E. R. Lippincott, J. Raman Spectrosc. 1, 305
`(1973).
`10. Mansel Davies, Some Electrical and Optical Aspects of Molecular
`Behaviour, Pergamon Press, Oxford (1965).
`11. N. L. Lavrik and Yu. I. Naberukhin, Opf. Spektrosk. 39, 1093
`(1975); Opt. Spectrosc. 39, 628 (1975).
`12. R. Mierzecki, Proceedings of the Fifth International Conference
`on Raman Spectroscopy, Freiburg, 1976, Hans Ferdinand Schulz
`Verlag D-7800 Freiburg im Breisgau.
`
`Received 19 October 1976
`
`© Heyden & Son Ltd, 1977
`
`
`
`JOURNAL OF RAMAN SPECTROSCOPY, VOL. 6, NO. 2, 1977
`
`79
`
`Merck Exhibit 2237, Page 6
`Mylan Pharmaceuticals Inc. v. Merck Sharp & Dohme Corp.
`IPR2020-00040
`
`

`

`Merck Exhibit 2237, Page 7
`Mylan Pharmaceuticals Inc. v. Merck Sharp & Dohme Corp.
`IPR2020-00040
`
`

`

`Liaison Hydrogene en Phase Liquide et
`Spectrornetrie Raman
`I1.F-Amines Primaires et Secondaires
`
`C. Perchard et J. P. Perchard
`Laboratoire de Spectrochimie MolCculaire, UniversitC Pierre et Marie Curie, 10 Rue Cuvier 75230 Paris Cedex 05, France
`
`Structure, intensity and depolarization ratio of NH or NH2 Raman bands of some primary and secondary amines
`have been studied in pure liquid state at different temperatures and in dilute CCI, solutions. The depolarization
`ratio and scattering activity, as in the case of alcohols previously studied, increase with self association. It confirms
`the change of the XH bond polarizability derivatives with hydrogen bond formation.
`
`INTRODUCTION
`
`Dans le cadre d’une Ctude de liaisons hydrogbne faibles
`par spectromCtrie Raman nous prisentons ici des
`rksultats obtenus sur le systkme NH.0.N relatif a deS
`amines primaires ou secondaires simples. Dans un
`travail prCc6dent’ concernant la bande vOH du systkme
`O-H..-O d’alcools liquides, deux rCsultats notables ont
`CtC obtenus: une structure B deux composantes due B
`une association en chaine des molCcules, et d’autre part
`un accroissement significatif de I’activitC de diffusion
`(45a” + 7 y ” ) et du rapport de dCpolarisation par
`autoassociation.
`Notre Ctude se divise en deux parties, la premikre
`relative B la description des bandes vNH ou vNH2 en
`phase liquide du point triple au voisinage du point
`critique, la seconde a des mesures d’intensitC sur ces
`m2mes bandes.
`Les amines primaires CtudiCes sont la mCthylamine et
`1’Cthylamine; les amines secondaires, la dimkthylamine,
`la dikthylamine (et les espkces deutkrikes ND corres-
`pondantes) et le pyrrole.
`
`PARTIE EXPERIMENTALE
`
`Les espkces hydrogknkes proviennent de la marque
`RhBne-Poulenc. Les composCs sont introduits par distil-
`lation sous vide dam la cellule de mesure. Les espbces
`deutCriCes ont CtC prCparCes par Cchanges successifs
`des chlorhydrates dans l’eau lourde. Le taux isoto-
`pique, contrB1C spectroscopiquement, est supCrieur B
`90%.
`La technique d’enregistrement des spectres a dCja CtC
`dCcrite prCc6demment.l Toutes les amines sont parfaite-
`ment stables dans le faisceau laser B I’exception du
`pyrrole pour lequel il est nCcessaire de travailler avec
`une faible puissance (50mW) et en renouvellant le
`contenu de la cellule toutes les heures environ.
`
`t Partie I: voir RCf. 1.
`
`@ Heyden & Son Ltd, 1977
`
`74 JOURNAL OF RAMAN SPECTROSCOPY, VOL. 6,
`
`NO.
`2, 1977
`
`DESCRIPTION DES BANDES
`vNH ET uNH,
`
`Amines secondaires
`Dimethylamine. L’kvolution des spectres Ivv et IVH est
`prCsentCe sur la Fig. 1. A tempkrature 6levCe la com-
`posante Ivv est symCtrique et de faible largeur
`caracteristique de vibrateurs NH libres. A tempkrature
`infCrieure, une seconde bande large apparait en Cpaule
`la prCc6dente vers les basses frCquences et se substitue
`progressivement a elle par refroidissement; elle corres-
`pond aux vibrateurs NH..-N perturbCs par formation de
`liaison hydrogbne. Au voisinage du point de fusion, la
`bande monomCrique a presque totalement disparu tan-
`dis que les composantes Ivv et IVH ont des maxima situCs
`respectivement 3247 cm-’ et 3258 cm-l. Au passage a
`la phase cristalline la structure a deux composantes
`subsiste, les maxima respectifs &ant situCs B 3215 et
`3238 cm-I a 170 K. L’interprCtation de l’ensemble des
`rCsultats est la suivante: comme il a dCja CtC observC en
`infrarouge,2 le degrk d’autoassociation est beaucoup
`plus faible pour les amines que pour les alcools de
`formule Cquivalente. La bande monomkrique (ou
`Cventuellement de bout de chaines) est observCe B
`tempCrature
`beaucoup
`plus
`base
`pour
`la
`dimkthylamine que pour I’alcool isoproprylique et ne
`disparait que vers 190 K au lieu de 360 K pour I’alcool.
`Le dkcalage entre Ivv et IVH observC alors pour la bande
`autoassociCe est interprCtC, comme dans le cas des
`alcools, par un effet de couplage entre vibrateurs NH;
`comme l’interaction entre vibrateurs NH est plus faible
`que celle entre vibrateurs OH, 1’Cclatement observC est
`ici beaucoup plus petit et n’apparait notablement qu’au
`voisinage du point de fusion. La continuit6 observCe
`dans la structure des bandes lors du passage 5 1’Ctat
`cristallin est la preuve d’un ordre B courte distance en
`phase liquide. L’absence de donnCes cristallographiques
`ne permet pas de prCciser s’il s’agit d’une association en
`chaines.
`Des mesures analogues ont CtC effectuies sur l’espbce
`deutCriCe (CH&ND, mais l’analyse des rCsultats est
`rendue difficile en raison d’une rksonance de Fermi
`
`Merck Exhibit 2237, Page 8
`Mylan Pharmaceuticals Inc. v. Merck Sharp & Dohme Corp.
`IPR2020-00040
`
`

`

`LIAISON HYDROGENE EN PHASE LIQUIDE ET SPECTROMETRIE RAMAN
`
`basse frkquence. Par ailleurs, au voisinage du point de
`fusion, la bande libre reste importante et la bande
`associCe apparait A 3263 cm-l. Sur le spectre du cristal,
`une seule composante fortement dCcalCe vers les basses
`frCquences apparait (3205 cm-’ B 220 K), tandis qu’un
`effet de dilution isotopique NH/ND B
`la mgme
`temperature permet d’observer un dCplacement de la
`bande vers les hautes frkquences (3216 cm-I).
`Pour ce composC, on conclut donc que les effets
`d’autoassociation sont faibles en phase liquide, le stade
`de polymkrisation ne dkpassant gukre celui de dimkre.
`L‘analyse du spectre du composC ND correspondant
`apparait plus complexe en raison d’une rksonance com-
`parable B celle mentionnke pour la dimCthylamine.
`Cependant on retrouve les principaux caractbres du
`(Fig. 4): Cquilibre conformationnel
`massif NH
`caractCrisC par un dCdoublement de la bande du
`monombre et dCcalage trbs prononcC de la bande de
`polymbre lors du passage B 1’Ctat cristallin (2365 cm-’
`contre 2391 cm-I).
`Pyrrole. Nous retrouvons our le pyrrole des rCsultats
`dCjB discutes par LautiC!
`Entre 300 et 200K, les
`spectres du composC liquide ou vitreux prdsentent des
`bandes larges, remplacCes B 1’Ctat cristallin par deux
`raies fines dues B un effet de couplage intermolCculaire.
`Dans notre Ctude Raman, nous observons de plus qu’B
`1’Ctat liquide ou vitreux la composante IVH se trouve
`dCcalCe de 8 cm-I au maximum vers les hautes
`
`K
`
`419
`
`2500
`2300
`C
`Figure 2. (CHJ2ND. Spectres IVv et IvH B differentes temperatures.
`
`L‘intensite des composantes lVH a Bte multiplide par 5. Largeur de
`fente spectrale 1.7 cm-’.
`
`I
`
`JOURNAL OF RAMAN SPECTROSCOPY, VOL. 6, NO. 2, 1977 75
`
`3400
`
`3200
`
`cm-’
`
`Figure 1. (CH&NH. Spectres Ivvet IvH B differentes temperatures.
`L‘intensite des composantes IvH a ete multipliee par 5. Largeurde
`fente spectrale 1,5 cm-’.
`
`entre la vibration vND et une combinaison vers
`2500cm-I observCe en phase liquide aussi bien qu’B
`1’Ctat g a ~ e u x . ~ L’evolution des spectres du liquide est
`prCsentCe sur la Fig. 2; B haute temperature, comme B
`1’6tat gazeux, la composante de haute frCquence est la
`plus intense, indiquant une contribution importante de
`la fondamentale vND B I’intensitC de cette bande. Par
`refroidissement la frCquence de la fondamentale dCcroit
`et I’intensitC de la bande de haute frCquence s’affaiblit
`progressivement pour devenir nCgligeable dans le
`spectre du cristal B 170 K. En raison de la complexit6 il
`parait difficile de discuter des positions relatives des
`composantes Ivv et IvH. Notons toutefois qu’au voisi-
`nage du point de fusion la composante IVH est dCcal6e
`vers les hautes frCquences d’une dizaine de cm-’ par
`rapport B la composante Ivv.
`Diethylamine. L’Cvolution des spectres de la bande
`vNH de la dikthylamine liquide se diffkrencie notable-
`ment de celle observCe pour la dimkthylamine. D’une
`part la bande correspondant au vibrateur NH libre se
`dCdouble aux temperatures ClevCes (Fig. 3) par suite de
`l’existence d’isombres de rotation 4 : B 416 K les deux
`composantes sont mesurCes B 3340 et 3327cm-l, la
`bande de haute frCquence s’aff aiblissant progressive-
`ment par abaissement de tempkrature. De cette obser-
`vation, on conclut donc que l’isombre thermodynami-
`quement le plus stable doit etre associC B la bande de
`
`Merck Exhibit 2237, Page 9
`Mylan Pharmaceuticals Inc. v. Merck Sharp & Dohme Corp.
`IPR2020-00040
`
`

`

`C. PERCHARD ET J. P PERCHARD
`
`suite d’une sensibilitC plus grande A l’association des
`molCcules. De plus
`il apparait une bande vers
`3180 cm-’, dCjh observCe par Wolff6 en absorption, et
`probablement attribuable B l’harmonique de la vibration
`6NH2 exaltke par rCsonance de Fermi avec la vibration
`v,. A 1’Ctat cristallin, quatre composantes apparaissent a
`3325,3265,3237 et 3179 cm-’.
`Methylamine. Des spectres analogues ont CtC obtenus
`pour la mCthylamine A 1’6tat liquide ainsi qu’A 1’6tat
`solide. L’interprCtation du spectre de cristal a pu Ctre
`faite6 en tenant compte de l’existence, prouvke par une
`Ctude cri~tallographique,~ de deux types de liaison
`hydrogbne et d’une rCsonance de Fermi avec le niveau
`2SNH2.
`
`MESURES D’INTENSITE DES
`BANDES vNH
`
`Comme nous I’avons fait pour les alcools, nous avons ici
`CtudiC 1’Cvolution du rapport de dCpolarisation et
`1’intensitC des bandes YNH des amines en fonction de
`1’Ctat physique et, par suite, de 1’Ctat d’autoassociation
`
`! I
`
`I
`
`I
`
`2500
`
`I
`
`2400
`
`I
`
`cm-1
`
`Figure 4. (C,H&Nd. Spectres/,,,,B differentes temperatures.
`Largeur de fente spectrale 3,3 cm-’.
`
`‘L
`
`*$
`
`K
`295
`
`A GK
`
`1
`3300
`
`I
`
`I
`3200
`
`1
`
`cm-‘
`
`~
`
`I
`
`I
`
`I
`3400
`
`Figure 3. (C2H&NH. Spectres Ivv et IVH B differentes tempkra-
`tures. L‘intensite des composantes lVH at ete multipliee par 10
`pourlesspectresB416et295 Ketpar5pourceluiB230 K. Largeur
`de fente spectrale 3,O cm-’.
`
`frCquences par rapport B la composante Ivv (Fig. 5).
`Comme pour le cristal, nous relions ce phCnombne B
`l’existence de couplages entre vibrateurs NH, associCs a
`un ordre A courte distance dans les phases dites
`dCsordonnCes.
`
`Amines primaires
`
`L’association de la mtthylamine et de 1’Cthylamine et la
`structure des bandes vNH2 correspondantes ont dCja CtC
`longuement discutCes par Wolff et ~ 0 1 1 . ~ a partir de
`rCsultats infrarouge et Raman.
`Ethylamine. A tempkrature Clevte (414 K), les deux
`bandes Y, et v, sont observkes respectivement vers 3387
`et 3334 cm-’ (Fig. 6)’ et correspondent aux vibrateurs
`NH2 non engagCs dans liaison hydrogbne. Lorsque la
`tempkrature s’abaisse jusqu’h 196 K les maximums des
`deux bandes dkcroissent, respectivement de 30 cm-’
`pour v, et 50 cm-’ pour vs; la bande correspondant ii v,
`s’klargit considtrablement et devient dissymttrique, par
`
`76 JOURNAL
`
`OF
`RAMAN SPECTROSCOPY, VOL. 6, NO. 2, 1977
`
`Merck Exhibit 2237, Page 10
`Mylan Pharmaceuticals Inc. v. Merck Sharp & Dohme Corp.
`IPR2020-00040
`
`

`

`LIAISON HYDROGENE EN PHASE LIQUIDE ET SPECTROMETRIE RAMAN
`
`I
`
`\
`
`
`
`~
`
`414 K
`
`zvv
`
`I V H
`
`I
`3450
`
`I
`3400
`
`I
`3350
`
`c