Exam 1 Flashcards
What type of waves does infrared spectroscopy measure?
Infrared waves
What does IR spectroscopy measure
The bond vibration frequencies; helps determine the structure of a compound.
Where is the fingerprint region?
Below 1500. Ignore this part of the graph.
What is the cm-1 of a carbon carbon single bond (sp3 hybridized)
1200 cm-1
Irrelevant because it falls within the fingerprint region
What is the cm-1 of a C-C double bond (hint: sp2 hybridized)
1660 cm-1
What is the cm-1 of a C-C triple bond? (Hint: sp hybridized)
<2200 cm-1. Usually will be 2140 to 2150.
What is the cm-1 of a conjugated C-C double bond (ex. aromatic carbon)
Approximately 1600 cm-1. Resonance/conjugation LOWERS the frequency compared to an isolated C-C double bond.
What is the cm-1 of a C-H bond on an sp3 hybridized C? (Hint: Alkane)
2800-3000 cm-1. Broad band
What is the cm-1 of an C-H bond on an sp2 hybridized C? (Hint: Alkene)
3000-3100 cm-1. HINT: There will also be a long stretch at 1642 cm-1 for the double carbon bond.
What is the cm-1 of an C-H bond on an sp hybridized C?
3300 cm-1. SHARP indent on graph. HINT: Will only show up with an asymmetrical alkyne. If the alkyne is symmetrical there is no peaks at 2119 cm-1 for the triple bond, or for the C-H stretch.
What is the shape of the O-H bond?
Around 3300 cm-1, with a broad and rounded tip.
What is the measurement for amines (N-H)?
3300 cm-1.
What do the peaks look like for a primary amine (RNH2)?
Broad with two sharp spikes, since there are two hydrogrens
What does the peak look like for a secondary amine (R2NH)?
Broad with one sharp spike.
What does the peak look like for a tertiary amine (R3N)?
There is no peak! Since there are no hydrogens the IR does not show a tertiary amine.
What is the measurement of a C-O double bond?
Simple ketones, aldehydes, and carboxylic acids absorb around 1710 cm-1.
Which of the three molecules with carbonyl groups (ketones, aldehydes, and carboxylic acids) has two C-H signals?
Aldehydes. Both are around 2700 and 2800 cm-1.
What is the measurement of the O-H stretch in carboxylic acid?
2500-3500 cm-1. Both a peak for the C-O double bond (1710 cm-1) plus this OH must be present to identify the carboxylic acid.
What is the measurement of esters (C=O + R/ OR)
Around 1735 cm-1.
What is the measurement of a C-N bond?
Around 1200 cm-1.
Irrelevant because its in the fingerprint zone
What is the measurement of a C-N double bond?
1660 cm-1.
What is the measurement of a C-N triple bond?
> 2200 cm-1. A nitrile (C-N triple bond) is GREATER than a C-C triple bond.
What are the top three strongest frequencies?
Alcohol(OH), amine (NH), and alkyne (triple C-C bond with the C of interest attached to a hydgrogen. Recall that this alkyne must be asymmetrical). All measure at around 3300 cm-1.
What does a hydrogen’s chemical shift depend on?
The atoms that are next to the carbon attached to the hydrogen. It is measured in ppm.
