IR Spectroscopy Flashcards
Larger frequencies (higher energies) are absorbed by…
-Bonds with a higher bond order
-Bonds between atoms with a larger mass difference
What is the critical reference value for the N-H/O-H region?
3250 cm-1
How do we differentiate between peaks in the N-H/O-H region?
-O-H peaks are typically strong to moderate and broad
-N-H peaks are typically moderate to weak and sharp
-C-H peaks are very sharp
What is the critical reference value for the C-H region?
3000 cm-1
How do you differentiate between peaks in the C-H region?
-sp3 is to the right of 3000
-sp2 is to the left of 3000
-Aldehyde is 2750 and 2850
What is the critical reference value for the C triple bond N/C triple bond C region?
2250 cm-1
How do you differentiate between peaks in the C triple bond N/C triple bond C region?
-Alkyne peaks are moderate to weak
-Nitrile peaks are strong to moderate
What is the critical reference value for the C=O region?
1715 cm-1
What is the range possible for C=O?
1800-1650
How do you differentiate peaks in the C=O region?
C=O peaks are typically strong and slightly broad
What is the critical reference value for the C=C region?
1600 cm-1
How do you differentiate between peaks in the C=C region?
-C=C peaks are typically strong to moderate and sharp
-Aromatic C=C is below 1600 cm-1
-Alkene C=C is above 1600 cm-1
What are critical reference values?
Center value of the FG range
List the approximate zone lines from left to right.
3200, 2700, 2000, 1650, 1400
What is the critical reference value for the C=O FG region?
1715 cm-1
How do you differentiate between peaks in the C=O region?
-Aldehyde has present of moderate C-H peak (2x below 3000)
-Carboxylic acid has presence of extremely broad O-H peak
Ester _____ vibrational energy by _____.
increases, 30 cm-1
Amide ______ vibrational frequency by _____.
decreases, 30 cm-1
Acyl halides/anhydrides ______ energy more than ____.
increase, 30
Conjugation decreases vibrational frequency by ______.
30 cm-1
Conjugation on both sides of the carbonyl decreases frequency by _____.
60 cm-1
_______ is strain free and “normal”.
cyclohexane
Ring strain increases vibrational energy by ______.
30 cm-1
More strain = ______.
higher energy
What is the stretching frequency of an anhydride?
1810 cm-1
What is the stretching frequency of an acid chloride?
1800 cm-1
What is the stretching frequency of an ester?
1735 cm-1
Resonance causes the bond to _____ and induction causes the bond to ______.
lengthen, shorten
