Where might the following compounds have IR absorptions? |...

Name: Problem 10, Chapter 12: Organic Chemistry
Uploaded: 2020-07-14T05:31:21-08:00
Duration: 5 min 53 s
Channel: Ian Kaigh
Description: Where might the following compounds have IR absorptions?

Key Concepts

Infrared Spectroscopy

Infrared spectroscopy is an analytical technique used to identify molecular structures by measuring the absorption of infrared light, which causes vibrational transitions in a molecule. It is widely used in chemistry because different bonds and functional groups absorb characteristic frequencies of IR radiation, allowing for qualitative and quantitative analysis of compounds.

Vibrational Modes

Vibrational modes refer to the ways in which the atoms in a molecule move relative to each other, including stretching, bending, twisting, and rocking motions. Each type of vibration typically occurs at specific frequencies in the IR region, and understanding these modes is essential for assigning IR absorption bands to corresponding molecular motions.

Functional Group Frequencies

Functional group frequencies are the characteristic IR absorption ranges associated with specific types of chemical bonds or groups within a molecule, such as carbonyl, hydroxyl, or alkene groups. These frequencies provide key diagnostic features that help in the identification and structural determination of organic compounds.

Wavenumber Scale

The wavenumber scale, measured in inverse centimeters (cm?¹), is used to express the frequencies at which IR absorptions occur. It is inversely proportional to wavelength and provides a convenient way to compare the energy of different vibrational transitions, facilitating the identification of functional groups based on their observed absorption bands in an IR spectrum.

Transcript

00:04 This is the answer to chapter 12, problem number 10 from the mcmurray organic chemistry textbook.

00:11 This problem gives us three different molecules and asks us where might they have ir absorptions? and so basically the way to answer this problem and problems like it is going to be to look at these molecules, decide what functionality there is in each of them or what bonds that.

00:34 There are that are going to give rise to ir signals, and then list where we would expect those signals to be.

00:45 So for a, we have an ester and an alken.

00:54 So the ester group is this.

00:59 The alken, obviously, is this.

01:02 And so the ester it's next to a double bond so we probably expect to see that at about 1715 wave number and then the alken we expect to see 1640 to 1680 okay so there's part a for part b for part b we have alkyne and we have an aldehyde and so aldehyde alkyne and so remember the alkyne is going to give rise to two different signals so the aldehyde should show at about 1730 wave number and then for the alkyne as i said we're going to have two different signals so for the alty we're going to have a c, triple bond c.

02:26 That's going to show at about 2 ,100 to 2260 or so.

02:38 And then we also have the alkyne.

02:47 Since this is a terminal alkyne, we're going to have the csp carbon bound to a hydrogen.

02:56 And so that is going to show.

02:58 At about 3 ,300 wave number.

03:04 So three signals for part b.

03:07 For part c, we have a lot going on.

03:09 We have an aromatic ring...