stuff to mem

IR: what region is the functional group region vs fingerprint region?

Functional group region: 4000-1500 cm-1 (use this to ID groups). Fingerprint region: below 1500 cm-1 (unique to each molecule, mostly not used for assigning).

IR: O-H stretch (alcohol)

3200-3600 cm-1, strong, BROAD (hydrogen bonding).

IR: O-H stretch (carboxylic acid)

2500-3300 cm-1, very broad, 'messy hump' that overlaps the C-H region. Also has a C=O near 1710.

IR: N-H stretch (amines)

3300-3500 cm-1. Primary (RNH2): TWO peaks. Secondary (R2NH): ONE peak. Tertiary (R3N): NONE. Sharper and weaker than O-H.

IR: sp3 C-H stretch

2850-3000 cm-1 (just BELOW 3000).

IR: sp2 C-H stretch (alkene or aromatic)

3000-3100 cm-1 (just ABOVE 3000).

IR: sp C-H stretch (terminal alkyne)

~3300 cm-1, strong and SHARP.

IR: aldehyde C-H stretch

Two peaks at ~2720 and ~2820 cm-1 (the 2720 shoulder is diagnostic). Along with C=O near 1725.

IR: C triple bond N (nitrile)

2210-2260 cm-1, medium, sharp.

IR: C triple bond C (alkyne)

2100-2260 cm-1, weak (can be absent in a symmetrical internal alkyne).

IR: C=O stretch range

1670-1780 cm-1, strong and sharp. Usually the easiest peak to spot.

IR: ketone C=O

~1715 cm-1.

IR: aldehyde C=O

~1725 cm-1 (plus C-H peaks at 2720 and 2820).

IR: ester C=O

~1735-1745 cm-1 (higher than ketone). Also strong C-O at 1000-1300.

IR: carboxylic acid C=O

~1710 cm-1, plus a very broad O-H at 2500-3300.

IR: amide C=O

~1650-1690 cm-1 (LOWER than ketone because of N resonance). Primary/secondary amides also show N-H at 3300-3500.

IR: acid chloride C=O

~1800 cm-1 (very high).

IR: anhydride C=O

TWO peaks, ~1760 and ~1820 cm-1.

IR: how does conjugation change C=O position?

LOWERS it by about 25-40 cm-1 (e.g., conjugated ketone ~1680 instead of 1715), because resonance weakens the C=O double bond.

IR: how does ring strain change C=O position?

RAISES it. Cyclohexanone ~1715, cyclopentanone ~1745, cyclobutanone ~1780.

IR: C=C stretch (alkene)

1620-1680 cm-1, medium/weak.

IR: aromatic C=C stretch

1450-1600 cm-1 (usually several peaks), plus sp2 C-H just above 3000.

IR: C-O stretch

1000-1300 cm-1, strong (alcohols, ethers, esters, acids).

IR: nitro group (NO2)

Two strong peaks: ~1550 (asymmetric) and ~1350 cm-1 (symmetric).

IR: C-Cl, C-Br stretches

C-Cl ~600-800 cm-1; C-Br lower still (~500-600). In the fingerprint region, rarely used.

IR: broad strong peak at 3300 and a strong peak at 1715. What functional groups?

Alcohol O-H plus ketone/aldehyde C=O (or, if the OH is VERY broad from 2500-3300, a carboxylic acid).

IR: strong peak at ~1715 cm-1

Ketone C=O (aldehyde ~1725, carboxylic acid ~1710 with broad OH).

IR: sharp peak at ~2250 cm-1

Nitrile (C triple bond N) or an alkyne.

IR: sharp peak at ~3300 cm-1

Terminal alkyne C-H (sharp). If broad, it is an O-H; if two sharp-ish peaks, a primary amine.

IR: strong peak at ~1740 cm-1

Ester C=O.

IR: strong peak at ~1650-1690 cm-1

Amide C=O (or conjugated ketone ~1680, or C=C ~1650).

IR: why is O-H broader than N-H?

Stronger hydrogen bonding in O-H gives a wider range of bond environments, so a wider, more intense band.

IR: which bonds absorb at higher wavenumber?

Stronger bonds and lighter atoms: triple > double > single; X-H bonds appear highest (O-H, N-H, C-H at 2700-3600).

IR: how to tell ketone from ester quickly?

Ester C=O is higher (~1740 vs ~1715) and esters show a strong C-O stretch at 1000-1300.

IR: how to tell an alcohol from a carboxylic acid?

Both have O-H, but the acid also has C=O (~1710) and the O-H is much broader (2500-3300).

1H NMR: what are the 4 pieces of info in a 1H NMR spectrum?

Number of signals (unique H environments), chemical shift (type of H), integration (ratio of H's), splitting (neighboring H's).

1H NMR: how do you count signals?

One signal per set of chemically equivalent H's. Use symmetry; H's related by a mirror plane or rotation are equivalent.

1H NMR: n+1 rule

A signal splits into n+1 peaks, where n = number of H's on ADJACENT carbons (3 bonds away). Applies only to non-equivalent neighbors.

1H NMR: peak ratios of a doublet, triplet, quartet, pentet

Doublet 1:1; triplet 1:2:1; quartet 1:3:3:1; pentet 1:4:6:4:1; (sextet 1:5:10:10:5:1).

1H NMR: alkyl CH3 (R-CH3)

~0.9 ppm.

1H NMR: alkyl CH2 (R-CH2-R)

~1.2-1.4 ppm.

1H NMR: alkyl CH (R3C-H)

~1.4-1.7 ppm.

1H NMR: allylic H (H-C-C=C)

~1.6-2.6 ppm.

1H NMR: H alpha to C=O (H-C-C=O)

~2.0-2.7 ppm.

1H NMR: benzylic H (H-C-Ar)

~2.3-2.7 ppm.

1H NMR: terminal alkyne H (C triple bond C-H)

~2-3 ppm (about 2.5).

1H NMR: H-C-N (amine neighbor)

~2.2-2.9 ppm.

1H NMR: H-C-X (halide neighbor)

~2.5-4.0 ppm. More electronegative X = more downfield (Cl ~3-4, Br ~2.7-4, I ~2-4).

1H NMR: H-C-O (alcohol, ether, ester O side)

~3.3-4.5 ppm (ethers and alcohols ~3.3-4; ester R-CO-O-CH ~4-4.5).

1H NMR: vinyl H (H-C=C)

~4.5-6.5 ppm.

1H NMR: aromatic H (benzene)

~6.5-8.5 ppm (benzene itself ~7.3).

1H NMR: aldehyde H (O=C-H)

~9-10 ppm. Often a small doublet or singlet.

1H NMR: carboxylic acid H (COOH)

~10-13 ppm, broad singlet.

1H NMR: alcohol O-H

~1-5 ppm, broad singlet, variable with concentration/solvent.

1H NMR: phenol O-H

~4-7 ppm, broad.

1H NMR: amine N-H

~1-5 ppm, broad singlet.

1H NMR: amide N-H

~5-9 ppm, broad.

1H NMR: D2O shake test

Add D2O: exchangeable protons (O-H, N-H, COOH) swap to D and the signal DISAPPEARS.

1H NMR: why are electronegative groups downfield?

They withdraw electron density (deshielding) so the H feels more of the external field and resonates at higher ppm.

1H NMR: why are aromatic and aldehyde H's so far downfield?

Ring current (aromatics) and C=O anisotropy plus electronegativity (aldehydes) strongly deshield them.

1H NMR: what does TMS do?

Reference standard set at 0 ppm. Upfield = lower ppm, shielded; downfield = higher ppm, deshielded.

1H NMR: ethyl group pattern (-CH2CH3)

CH3 triplet (3H, ~1 ppm) and CH2 quartet (2H, ~2-4 ppm depending on neighbor).

1H NMR: isopropyl group pattern

Doublet (6H, ~1 ppm) and septet (1H, ~1.5-4 ppm).

1H NMR: tert-butyl group pattern

Singlet, 9H, ~1.0-1.3 ppm.

1H NMR: methyl on a ketone or ester (CH3-C=O)

Singlet, 3H, ~2.1 ppm.

1H NMR: methyl ester OCH3

Singlet, 3H, ~3.7 ppm.

1H NMR: methoxy on aromatic (Ar-OCH3)

Singlet, 3H, ~3.8 ppm.

1H NMR: para-disubstituted benzene pattern

Two doublets (2H each) in the 6.5-8 region (AA'BB' pattern) for two different substituents.

1H NMR: monosubstituted benzene pattern

Integrates to 5H, a multiplet around 7.1-7.4 ppm.

1H NMR: coupling constant J for trans vs cis alkene H's

Trans ~11-18 Hz (larger); cis ~6-15 Hz; geminal (same carbon) ~0-3 Hz. Typical vicinal sp3 ~6-8 Hz.

1H NMR: what does integration tell you?

The RELATIVE number of H's in each signal (ratio). Scale to the total H count in the formula.

1H NMR: singlet means what?

No H's on adjacent carbons (or neighbors that are chemically equivalent / exchangeable like OH).

1H NMR: why doesn't an OH usually split its neighbors?

Rapid proton exchange averages out the coupling, so O-H is a broad singlet and neighbors are not split by it.

1H NMR: diastereotopic vs enantiotopic H's

Diastereotopic H's (e.g., CH2 next to a stereocenter) are NOT equivalent: different signals. Enantiotopic H's are equivalent in achiral solvent.

13C NMR: what does number of signals tell you?

Number of UNIQUE carbons (symmetry reduces count). Signals are usually singlets in proton-decoupled spectra.

13C NMR: alkane carbon (sp3 C-C)

~0-50 ppm.

13C NMR: C-N (amine carbon)

~30-60 ppm.

13C NMR: C-O (alcohol, ether carbon)

~50-90 ppm.

13C NMR: C-X (halide carbon)

~10-70 ppm depending on the halogen (Cl ~ 40-70; I much lower).

13C NMR: alkyne carbons

~65-90 ppm.

13C NMR: alkene carbons (C=C)

~100-150 ppm.

13C NMR: aromatic carbons

~110-160 ppm (typically 120-140).

13C NMR: nitrile carbon (C triple bond N)

~115-125 ppm.

13C NMR: carboxylic acid, ester, amide C=O

~160-185 ppm.

13C NMR: ketone or aldehyde C=O

~190-220 ppm (ketones ~205-220, aldehydes ~190-200).

13C NMR: DEPT-135 rules

CH3 and CH point UP (positive); CH2 points DOWN (negative); quaternary C (no H) does NOT appear. DEPT-90 shows only CH.

Degrees of unsaturation (DoU) formula

DoU = (2C + 2 + N - H - X) / 2. Each ring or pi bond counts 1 (C=C = 1, C=O = 1, C triple bond = 2, benzene = 4). O and S are ignored.

Mass spec: M+2 pattern for bromine

M and M+2 peaks in ~1:1 ratio (79Br and 81Br).

Mass spec: M+2 pattern for chlorine

M and M+2 peaks in ~3:1 ratio (35Cl and 37Cl).

Mass spec: nitrogen rule

An ODD molecular ion mass means an ODD number of nitrogens; an even mass means zero or an even number of N.

List common STRONG BASES (E2 reagents)

NaOH, KOH, NaOMe, NaOEt, KOtBu (bulky), NaH, NaNH2, LDA (bulky), n-BuLi / RLi, Grignards RMgX, DBU / DBN (bulky, non-nucleophilic).

List common STRONG NUCLEOPHILES

HO-, RO- (MeO-, EtO-), HS-, RS-, CN-, N3-, I-, Br-, Cl- (in polar aprotic), RC triple bond C- (acetylides), NH3 / RNH2 (neutral amines), PPh3, H- (from NaBH4/LiAlH4), RMgX / RLi, enolates.

List STRONG NUCLEOPHILES that are WEAK BASES (best for SN2)

I-, Br-, Cl-, HS-, RS-, N3-, CN-, PPh3, RCOO- (moderate). Use in polar aprotic solvent for SN2.

List STRONG BASES that are POOR nucleophiles (bulky, favor E2)

KOtBu, LDA, DBU, DBN, NaH. Bulk blocks attack at carbon but they still grab protons.

List WEAK BASES / WEAK NUCLEOPHILES (SN1/E1 conditions)

H2O, CH3OH, EtOH, ROH, CH3COOH (acetic acid), HCOOH, TFE (CF3CH2OH). Usually the solvent (solvolysis).

Very weak bases (conjugate bases of strong acids)

I-, Br-, Cl-, HSO4-, TsO-, MsO-, TfO-, ClO4-, NO3-. These are stable and make excellent leaving groups.

List GOOD LEAVING GROUPS

I-, Br-, Cl-, TsO- (tosylate), MsO- (mesylate), TfO- (triflate), H2O (from protonated ROH), N2 (from diazonium), HSO4- / ROSO3-.

Rank leaving group ability for the halides

I- > Br- > Cl- >> F-.

Rank leaving group ability of sulfonates vs halides

TfO- (triflate) > TsO- ~ MsO- > I- > Br- > Cl- >> F-. (Triflate is among the best leaving groups.)

List BAD LEAVING GROUPS

HO-, RO-, NH2-, RNH-, R- (carbanions), H-, F-. They are strong bases (unstable anions). Must be activated first.