Infrared spectrum of n-heptane

In summary, the conversation discusses the problem of calculating the transmittance of blackbody radiation through liquid n-heptane, which has significant absorption peaks at 3.5, 7.0, and 14.0 micrometers. The issue is that a significant portion of the blackbody radiative energy falls outside of this range at higher and lower temperatures. To solve this problem, the speaker used a computer program to approximate the IR wavelengths where an alkane hydrocarbon can have significant spectral peaks based on C-C and C-H bond strengths. They also mention a website that has data up to 500 cm-1, which is the lower limit for vibrational absorption of organic molecules. This information helped solve the problem.
  • #1
hilbert2
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I have a work assignment where I'm supposed to calculate the transmittance of blackbody radiation through liquid n-heptane, and I have data of the heptane's absorption coefficient on the wavelength interval from 2.6 to 15 micrometers (it has significant peaks at about 3.5 ##\mu##m, 7.0 ##\mu##m and 14.0 ##\mu##m). The problem is, a significant part of the blackbody radiative energy is at wavelengths under 2.6 ##\mu##m at high temperatures and at wavelengths over 15 ##\mu##m at lower temperatures. I managed to get a correct-looking result for high temperatures by assuming that there's no significant absorption maxima in the interval from visible light to 2.6 ##\mu##m (of course there's none at visible range as it's a colorless liquid), but I'm not that sure about the long-wavelength range.

Is there some computer program or some simple approximative calculation that could predict, on the basis of the C-C and C-H bond strengths, the approximate IR wavelengths where an alkane hydrocarbon can have significant spectral peaks?

thanks,
Hilbert2
 
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  • #3
Thanks, that one seems to have data up to 500 cm-1 (or 20 ##\mu##m wavelength), so it's better than what I had.
 
  • #4
hilbert2 said:
Thanks, that one seems to have data up to 500 cm-1 (or 20 ##\mu##m wavelength), so it's better than what I had.
That's basically the lower limit (in terms of energy) of vibrational absorption for organic molecules.
 
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  • #5
Ok, good, that solves the problem then.
 

1. What is the infrared spectrum of n-heptane?

The infrared spectrum of n-heptane is a graph that shows the intensity of infrared light absorbed by the molecule at different wavelengths. It is unique to n-heptane and is used to identify the molecular structure and functional groups present in the compound.

2. How is the infrared spectrum of n-heptane obtained?

The infrared spectrum of n-heptane is obtained through a technique called infrared spectroscopy, which involves passing infrared light through a sample of n-heptane and measuring the amount of light absorbed at different wavelengths. This data is then plotted on a graph to create the spectrum.

3. What information can be obtained from the infrared spectrum of n-heptane?

The infrared spectrum of n-heptane can provide information about the functional groups present in the molecule, such as C-H, C-C, and C=C bonds. It can also give insights into the molecular structure and help in identifying impurities or contaminants in a sample of n-heptane.

4. How does the shape of the infrared spectrum of n-heptane differ from other compounds?

The shape of the infrared spectrum of n-heptane is unique to this specific compound and can be used to distinguish it from other compounds. The positions and intensities of the peaks in the spectrum are characteristic of n-heptane and can be used for identification purposes.

5. Can the infrared spectrum of n-heptane be used for quantitative analysis?

Yes, the infrared spectrum of n-heptane can be used for quantitative analysis to determine the concentration of n-heptane in a sample. The intensity of the peaks in the spectrum is directly proportional to the concentration of the compound, making it a useful tool for quantitative measurements.

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