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Infra red and raman

The X-H stretching frequency in the IR (and Raman) spectrum is dependant on the identity of X, i.e., O-H = 3610 - 3640 cm -1 and N-H = 3400 - 3500 cm -1 . However, the ν(X-H) is shifted to lower energy (lower frequency) as a consequence of hydrogen bonding. In addition, while non-hydrogen bonded X-H stretches are sharp, the presence of hydrogen bonding results in the peak being broadened. Figure X demonstrates both these effects. The O-H stretch for dilute n BuOH in CCl 4 is a sharp peak at 3650 cm -1 due to the lack of hydrogen bonding between the two components ( [link] a), and the presence of hydrogen bonding between n BuOH and n BuOH is limited by the dilution. By contrast, a dilute solution of n BuOH in Et 2 O results in a shift to lower frequency and a significant increase of peak width ( [link] b) as a result of fairly strong O-H ... O bonds. Finally, a dilute solution of n BuOH in NMe 3 results in a further shift to 3250 cm -1 and a very broad peak ( [link] c). The broadening of the peaks is due to the distribution of X-H distances within a X-H ... Y hydrogen bond.

Schematic representation of the O-H stretch region in the IR spectra of a dilute solution of n BuOH in (a) CCl 4 , (b) Et 2 O, and (c) NEt 3 .

Nmr

The presence of hydrogen bonding results the shift to higher ppm (lower frequency) of the 1 H NMR resonance for the proton. This shift is due to the decrease in shielding of the proton. A dilute solution of n BuOH in CCl 4 shows a resonance typical of a non-hydrogen bonded compound ( [link] a), while that for n BuOH in NMe 3 ( [link] b) shows a significant low field shift. Very strong intra or intermolecular hydrogen bonded species show a very large 1 H NMR shift (e.g., [link] c).

Schematic representation of the relative shift of the O H resonance for (a) n BuOH in CCl 4 , (b) n BuOH in NEt 3 , and (c) concentrated acetic acid.

Effects of hydrogen bonding

Physical effects

The presence of intermolecular hydrogen bonding provides additional attractive forces between molecules. Thus, properties that depend on intramolecular forces are affected.

Liquids with significant hydrogen bonding exhibit higher boiling points, higher viscosity, and higher heat of vaporization (ΔH v ) as compared to analogous compounds without extensive hydrogen bonding. For solids the presence of hydrogen bonding results in an increase in the melting point of the solid and an increase in the associated heat of fusion (ΔH f ).

The archetypal case for the effect of hydrogen bonding is the melting and boiling points of the hydrides of the Group 16 elements, i.e., H 2 E. For a series of analogous compounds with the same molecular structure it would be expected that the boiling points would be related to the molecular mass. However, as can be seen from [link] , the melting and boiling points of water are anomalously higher than those of its heavier analogs. In fact from [link] it is clear that just considering H 2 S, H 2 Se, and H 2 Te, the expected trend is observed, and it is similar to that for the Group 14 hydrides (CH 4 , SiH 4 , etc). Therefore, water must have additional intermolecular forces as compared to its heavier homologs. This observation is consistent with the strong hydrogen bonding in water, and the very weak if nonexistent hydrogen bonding in the sulfur, selenium, and tellurium analogs.

Questions & Answers

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s. Reply
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Devang Reply
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s.
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Abhijith Reply
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s. Reply
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Harper
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SUYASH
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s. Reply
of graphene you mean?
Ebrahim
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Ebrahim
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s.
Graphene has a hexagonal structure
tahir
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Cied
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Cied
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I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
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Porter
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what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
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AMJAD
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AMJAD
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Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
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Azam
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I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
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Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Hydrogen. OpenStax CNX. Sep 28, 2009 Download for free at http://cnx.org/content/col10984/1.4
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