Lab 5: Spartan IR

Objective: The purpose of this lab is to gain a deeper understanding of infrared spectroscopy through computational methods. In the lab, we will create models and determine the IR of three organic structures, two that were provided for us, and one that was a student designed molecule. Finally, the completed models will be uploaded for review into our lab

Methods:

• What is “ground state”, which we are using compared to “excited state”, which we are not.

The "ground state" is the lowest possible energy form of an atom. The "excited state" is when an atom has more energy than its ground state.

• What is “Density Functional Theory” which we are using.  

An electronic structure calculation is used to calculate the electronic structure of atoms and molecules.

• What are “long range dispersive interactions"?  This is the wB97X-D setting.

"Long Range" dispersive interactions are weak attractive forces that happen at long distances.

• What is a  6-31G function?

Notation that implies that each of the inner atomic shells is represented by a single six-Gausian contraction.

Above is an image of the the field calculation setting used for all three of the molecules analyzed within spartan. 

2-methylnon-6-ene-4-ol:

The IR for 2-methylnon-6-ene-ol indicated the presence of both alkene and alkane character with moderate and strong peaks noted from 2700-2800 cm-1, 2800-2900 cm-1, and 2900-3000 cm-1. Based on the known chemical formula of the molecule of study, the moderate peak absorbed at around 3600-3700 cm-1 was interpreted to be indicative of an OH functional group despite being shifted above the expected IR absorbance range from 3200-3500 cm-1. This is because the Spartan software has a known tendency to provide IR values higher than the expected literature values. There were several small peaks from within the fingerprint region, but as these are outside of the ranges we typically interpret for this course, they were disregarded in the analysis today.

7-cyano-octanoate: 

The IR for my chosen chemical, 7-cyano-octanoate,  had an IR with mostly weak character. There were peaks with weak character from 1500-1600 cm-1 and moderate character from 1600-1750 cm-1, likely consistent with the alkene character present within the molecule. There was a very weak peak at 1750-2000 cm-1 that is in the range of an ester group but not consistent with the typical presentation of the strong peak we would normally expect for an ester group. A weak peak was seen from 2250-2350 cm-1 and 2880-2900 cm-1. Either of these may be consistent with the nitrile character of the molecule as spartan has a tendency to shift the expected IR ranges above their known literature values. Another weak peak was noted from 2900-3000 cm-1, consistent with an alkane character. There were several peaks from within the fingerprint region, but as these are outside of the ranges we typically interpret for this course, they were disregarded in the analysis today.

Due to the lack of strength present in the IR despite several known functional groups with expected strong IR character within the chemical formula of the expected compound, future experimentation and repeat of IR may be useful.

Post Lab: None.