CHM247H1 Study Guide - Summer 2018, Comprehensive Midterm Notes - .Tl, Straight-Six Engine, Society Of Jesus
CHM247H1
MIDTERM EXAM
STUDY GUIDE
Fall 2018
CHM247
Lecture Topic 1
Degrees of Unsaturation, IR, NMR
Degrees of Unsaturation
eery loss of H’s = DOU
CnH2n+2 → CnH2n
ring = 1 DOU
double bond = 1 DOU
triple bond = 2 DOU
*in a molecule, count rings & double/triple bonds
*with a chem formula, use DOU formula
Infrared Spectroscopy
IR radiation has lower frequency, longer wavelength than red light
warmer object → more IR emitted → used in thermography for diagnosis of tumours
How does IR spectroscopy work?
IR causes increased bond stretching vibrations (and bending, but stretching more important)
IR active: vibrational stretching that changes the dipole moment
* no change in dipole = no IR signal
stronger bonds, higher frequency
lighter atoms, higher frequency
IR light absorbed if in resonance with bond vibration
or exact multiple (2x, 3x, 4x)
Notable points on IR
O-H H-bonding little, a lot, varies → more H-bonds, weaker O-H bond, (-) frequency, broad signal
C=C (benzene) conjugated → (-) s-character → (-) K, (-) wavenumber than other C=C
C-H H light → (+) vibration, (+) freq, (+) wavenumber, strong, sharp signal
s-character sp > sp2 > sp3 (more s, stronger bond, higher freq)
N-H (1o) can have asymmetric and symmetric stretching, assymetric more energy, higher freq, two peaks
C=O (acid anhydride) also has asymm/symm
conjugated bonds -O-C=O, resonance, less s-character, shift lower freq
induction effect Cl-CH=O, electro(-)ve atom moves e- from O to strengthen C=O
find more resources at oneclass.com
find more resources at oneclass.com
Nuclear Magnetic Resonance (NMR) Spectroscopy
Elucidate structures!
MRI! Radiowaves to body, non-invasive diagnoses
How does NMR work?
Nuclei (+) with e- (-) around them, spinning → local magnetic field
Can apply external magnetic field
Nuclei can be spin-aligned or spin against the external field
Resonance: when spin-aligned nucleus is spin-flipped with correct radiowave → aborbs to flip, detected in NMR spectrum
Every unique 1H and 13C atom = peak
1H spectrum has small peaks in large peaks
13C spectrum does not have small peaks in large peaks
1H NMR
Chemical Equivalence
Hs i same env = one peak
• symmetrical molecules
• Hs o sae ao unless next to chiral center, alkene)
• phel Hs usuall ultiplet ~
Chemical Shift
Normalized relative to TMS, therefore independent of magnetic field strength
• TMS, more shielded than almost all organic compounds
Between 0-12 ppm
Shielding: e-s around proton create magnetic field, if opposite applied field, will reduce Beffective (apparent field) = Bapplied - Blocal
6 regions
1. ost deshielded: aoli aid Hs, aldehde Hs
2. aromatic
3. alkene/vinylic
4. next to electronegative atom
5. next to double/triple bonds (allylic, benzylic)
6. most shielded: alkane
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Degrees of unsaturation e(cid:448)ery loss of (cid:1006) h"s = (cid:1005) dou. Cnh2n+2 cnh2n ring = 1 dou double bond = 1 dou triple bond = 2 dou (cid:2160)(cid:2171)(cid:2177)=[(cid:4666)(cid:2779)(cid:2159)+(cid:2779)(cid:4667) (cid:4666)(cid:2164)(cid:4667)+(cid:2163)(cid:2200)(cid:2197)(cid:2203)(cid:2198) (cid:2178) (cid:2163)(cid:2200)(cid:2197)(cid:2203)(cid:2198) (cid:2178)(cid:2165)(cid:2165)] (cid:2160)(cid:2171)(cid:2177)=[(cid:4666)(cid:2779)(cid:2159)+(cid:2779)(cid:4667) (cid:4666)(cid:2164)(cid:4667)+(cid:4666)(cid:2170)/(cid:2172)(cid:4667) (cid:4666)(cid:2162)/(cid:2159)(cid:2194)/(cid:2158)(cid:2200)/(cid:2165)(cid:4667)] (cid:2779) (cid:2779) *in a molecule, count rings & double/triple bonds. Ir radiation has lower frequency, longer wavelength than red light warmer object more ir emitted used in thermography for diagnosis of tumours (cid:2161) (cid:4666)(cid:2187)(cid:2196)(cid:2187)(cid:2200)(cid:2189) (cid:2197)(cid:2188) (cid:2198)(cid:2190)(cid:2197)(cid:2202)(cid:2197)(cid:2196)(cid:4667)=(cid:2190)(cid:2188)=(cid:2190)(cid:2185) (cid:2205)(cid:2183)(cid:2204)(cid:2187)(cid:2196)(cid:2203)(cid:2195)(cid:2184)(cid:2187)(cid:2200)=(cid:2778) Ir causes increased bond stretching vibrations (and bending, but stretching more important) Ir active: vibrational stretching that changes the dipole moment. * no change in dipole = no ir signal stronger bonds, higher frequency lighter atoms, higher frequency. Ir light absorbed if in resonance with bond vibration or exact multiple (2x, 3x, 4x) H-bonding little, a lot, varies more h-bonds, weaker o-h bond, (-) frequency, broad signal conjugated (-) s-character (-) k, (-) wavenumber than other c=c. Cl-ch=o, electro(-)ve atom moves e- from o to strengthen c=o.
