DOC PREVIEW
UIUC CHEM 203 - Solvachromic Dye lab

This preview shows page 1-2-3 out of 10 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 10 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 10 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 10 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 10 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Solvatochromic Dye: Exploring UV-Vis, IR, and NMR SpectroscopyIntroductionIn this lab, the ultimate goal is the determination of seven unknown solvents by collecting data from a spectrophotometer. The other main goals of this experiment are to obtain UV-Vis spectral data using a diode array of a spectrophotometer, analyze providedInfrared (IR) spectra for seven unknown organic molecules, analyze provided 1H nuclear magnetic resonance (NMR) spectra for seven unknown organic solvents, and use solvametric properties of Brooker’s merocyanine to rank the polarities of seven unknown solvents using spectral data1. A possible detailed list of the solvents that will be determined can be found in the table of reagents. The main concept of this lab is spectroscopy. This is using a light to probe the molecular structure of a sample. There are different types of spectroscopy that will be utilized in thislab. The first type is UV-Vis Spectroscopy. This type of spectroscopy introduces light to asample over a ranger of wavelengths1. The percentage of light transmitted can be seen in the following equation-log(%T/100) = Abs (1)%T is the transmittance and Abs is the absorbance. The absorbance vs. wavelength can beplotted and lambda max can be seen in this area. This is not very useful in determining unknown solutions, therefore Brooker’s merocyanine to determine these solutions. This merocyanine is an organic complex molecule that is soluble in many different solvents1. This is very sensitive to changes in polarity. These color changes can then be observed and data can be gathered about solvatochromism. This is when a compound shows a significant change in absorption when a solvent is dissolved1. Absorbance of light can also be correlated to energy of transition. The transition energy can be given by the following equationET = hcNA/ λmax(2)λmax is the max wavelength absorbed, h is Planck’s constant, c is the speed of light and Na is Avagadros constant.. Also the transition energy for an electron can be varied making the max lambda vary. This is most stable for a nonpolar solvent and will be smallest for this type of solvent. Also a Zwitterion is a molecule whose ionic charges add to give overall neutrality. With Brooker’s solution, the energy of transition In a polar solvent is less than nonpolar. This is the definition of “blue shift” or “Hypsochromic Shift”.The next kind of spectroscopy is Infrared. Infrared is when a sample is irradiated with light over a range of frequencies and absorbance’s in the infrared electromagnetic spectrum1. The absorbance is measured by a correspondence of a certain frequency with avibrational mode of the molecule. A vibrational mode of energy can be described as the simple harmonic oscillations of atoms about the equilibrium position of a bond in the x, y, z plane. These vibration modes correspond to a certain frequency. The photons are absorbed and the molecule begins to vibrate.. The frequencies of these are reported in wave numbers which can be given by the following equationWave numbers = ν / cWhere “ν” is the frequency and “c” is the speed of light. These will give rise to absorbance bands. The final kind of spectroscopy used is nuclear magnetic resonance (NMR) spectroscopy. This can be found by observing the 1H molecule or the probe structural information of the 13C molecule. For a 1H molecule they have an overall positive charge creating a magnetic field. When they are put into a magnetic field they all have about the same direction as the external NMR signal. An NMR signal is a measure of how the external field changes the moment vectors relative to the field1. Shielding can also occur in protons which is when other atoms block magnetic field from these atoms. The more shielding or deshielding (when protons are near other highly electronegative atoms) that is shown can be assigned upfield or down field in the spectrum. The location is known as the shift or ∂. This is given by parts per million for a peak on a spectrum. A proton in a nucleus will display (N+1) peaks in its signal. N is the number of nuclei affected by the signal. This can be used to determine how many hydrogen atoms are in a molecule.These chemistry concepts and the concept of spectroscopy can be seen in chemistry in the real world. Spectroscopy dyes were used in in the detection of biodiesel in diesel. The Solvatochromic dye was used in order for the direct simple detection2. This is used in several industries. Also this kind of process was used to detect low concentration of organiccompounds3. Finally this type of spectroscopy can show intramolecular charge transitions showing emission through the visible spectrum in many different types of experiments4.1.) Calculate the ET value for each of the solvents, then rank them in order of increasing polarity using these transition energy values. Why did you rank them in the order that you did? Be specific in your argument about how the properties of Brooker’s merocyanine allowed you to reach these conclusions. Solution Color withBrooker’sMeroyaninein bottleColor withBrooker’smerocyaninein test tubeλmax (nm) ET (KJ) PolarityRankA DarkMagentaPink 544 219.774 5B Dark Purple Dark purple 568 210.679 Least Polar7C Yellow Light/paleyellow375 319.108 Most Polar1D Bright red Peach/ lightyellow399 299.913 3E Dark Red Reddishorange523 228.806 4F Bright purple Very palepurple552 216.785 6G Dark Orange Orange 394 303.719 2The polarity was ranked from most polar (1) to least polar (7). This was done by looking at the calculated values for the λmax, and also the color with the merocyanine in it. The color that is closer to violet in the spectrum has the higher blue shift and therefore has a lower polarity. This is because the wavelength is shifted toward the shorter blue wavelength. Also the one that has the highest wavelength also is the least polar. The reason for this is because of the blue shift is because the merocyanine is more polar for a transition state and therefore when the polar solvent is added it is destabilized and the wavelength of light to the energy of transition in a polar solvent rather than a nonpolar solvent. Because of this there will be a lower ET associated with a higher wavelength given by equation number 2 in the introduction.2.) An IR spectrum has been provided for each solvent (no IR is provided for solvent C). Using what you have learned in lab, as well as outside resources, identify


View Full Document
Download Solvachromic Dye lab
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Solvachromic Dye lab and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Solvachromic Dye lab 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?