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OChem II

IR Values

TermDefinition
As bond strength increases, wavenumber _______. Increases
As mass of the molecule increases, wavenumber _______. Decreases
Area for N-H, C-H, and O-H bonds and why 4000-2500, higher than triple bonds because of H's low mass
Area for C triple bond N and C triple bond C 2500-2000
Area for C=O, C=N, and C=C 2000-1500
Alkane IR All C-H peaks will be BELOW 3000 when sp3 (C-H will be ABOVE when sp2 because then there is a double bond near a C-H)
Alkene IR Sharp C-H absorption ABOVE 3000 (because double bond) in C-H cluster and a small C=C absorption around 1650
Alkyne IR Sharp absorption around 3300 for a C-H bond a bit away from C-H cluster and a small C=C absorption around 2200
C-H stretching wavenumber ("energy") ______ going from alkanes -> alkenes -> alkynes because _____. Increases, bond strength increases
Steps for understanding IR and discerning molecule identity 1. Given molecular formula -> figure out degree unsaturation if any to draw up possible structures (alkene/alkyne bonds) 2. View IR and narrow it down: Remember that each absorption is a particular BOND, don't think about the full molecule.
The higher the electronegativity of a bond, the _____ the wavenumber. Higher
Equation for saturation with just C and H 2n + 2 when n=C
Equation for saturation with C, H, and N 2n + 1 when n=C+N
Amine IR Low, nonsharp or broad, absorption around 3300-3500. The number of peaks in it show the number of N-H bonds (2 peaks=NH2)
Equation to find degree unsaturation of alcohol (C,H, and O) Ignore the O: 2n+2 when n=C
Alcohol IR Broad peak ABOVE 3000 from the O-H
C=O (carbonyl) IR Sharp, usually most notable peak
Carboxylic acid IR C=O absorption around 1700 and an O-H that frequently overlaps with C-H cluster
Ester IR C=O absorption around 1735-1800 with no O-H absorption. Will be like 10 higher than ketone C=O absorption
Aldehydes Will have "Fangs" around 100 apart with nearly the same intensity. ONE WILL BE BELOW 2800, then look for one 100 greater than it. Will be clearly seen with sp2 C-H, but partially covered with sp3
Created by: RunningMads
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