🧪 Chemistry

Chemistry, quick reference

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Thermochemistry (91390)

Enthalpy from bonds ΔH = Σ(bonds broken) − Σ(bonds formed) Hess (formation) ΔH<sub>r</sub>° = ΣΔH<sub>f</sub>°(products) − ΣΔH<sub>f</sub>°(reactants) Gibbs free energy ΔG = ΔH − TΔS (feasible if ΔG < 0) Change-over temperature T=\frac{\Delta H}{\Delta S}\quad(\Delta G=0)

Aqueous equilibria (91392)

Water K<sub>w</sub> = [H⁺][OH⁻] = 1.0×10⁻¹⁴ pH pH = −log[H⁺] ; pH + pOH = 14 Weak acid K_a=\frac{[\ce{H+}][\ce{A-}]}{[\ce{HA}]}\qquad [\ce{H+}]=\sqrt{K_a c} Buffer \mathrm{pH}=\mathrm{p}K_a+\log\frac{[\ce{A-}]}{[\ce{HA}]} Solubility product K<sub>s</sub> = [Aⁿ⁺]ˣ[Bᵐ⁻]ʸ ; precipitate if Q > K<sub>s</sub>

Redox (91393)

Cell potential E°<sub>cell</sub> = E°<sub>cathode</sub> − E°<sub>anode</sub> (>0 = spontaneous) Half-equation (acid) balance atom → O with H₂O → H with H⁺ → charge with e⁻ OIL RIG Oxidation Is Loss, Reduction Is Gain (of e⁻)

Organic: naming & conditions (91391)

GroupSuffix/prefix
carboxylic acid-oic acid
ester-yl -oate
amide-amide
nitrile-nitrile
aldehyde-al
ketone-one
alcohol-ol
amine-amine/amino
alkene-ene
haloalkanehalo-
TransformationReagent / conditions
alkene → alcoholH₂O, H⁺
alcohol → alkeneconc H₂SO₄, Δ
haloalkane → alcoholNaOH(aq), warm
haloalkane → nitrileKCN / ethanol
haloalkane → alkeneKOH / ethanol, Δ
1° alcohol → aldehydeK₂Cr₂O₇/H⁺, distil
aldehyde → acidK₂Cr₂O₇/H⁺, reflux
2° alcohol → ketoneK₂Cr₂O₇/H⁺, reflux
nitrile → amineH₂/Ni
acid + alcohol → esterconc H₂SO₄

Spectroscopy: IR (91388)

Bondcm⁻¹
O–H alcohol3200–3550 broad
O–H acid2500–3300 v.broad
N–H amine/amide3300–3500 (amide = 2 peaks)
C–H alkane2850–3000
C=O acid chloride1785–1815
C=O ester1735–1750
C=O aldehyde1720–1740
C=O ketone1710–1720
C=O acid1705–1720
C=O amide1630–1695
C=C alkene1630–1680
C–O1000–1300
C–N1000–1250
C–Cl600–800
C–Br500–600

Spectroscopy: ¹³C NMR & MS (91388)

¹³C δ (ppm)Carbons in this region
0–15CH₃CH₂–
15–30CH₃–
20–35–CH₂–
30–60C–N, C–Cl, C–Br, C–C=O
50–70C–O
60–90C≡C
100–150C=C
160–185C=O in acids, esters, acyl chlorides, amides
180–220C=O in aldehydes and ketones
Fragment m/zIon
15CH₃⁺
17OH⁺
28CO⁺
29CH₃CH₂⁺ / CHO⁺
30CH₂NH₂⁺
31CH₃O⁺ / CH₂OH⁺
43C₃H₇⁺ / CH₃CO⁺
44CONH₂⁺
45COOH⁺ / CH₃CHOH⁺ / CH₃CH₂O⁺
57C₄H₉⁺
Mass lostGroupIndicates
1H–COOH / –CHO / –NH– / sometimes –OH
15CH₃–CH₃
17OH–COOH / –OH
18H₂O–OH (alcohol)
29CH₃CH₂ or CHO–CH₂CH₃ / –CHO
43CH₃COCH₃CO–

Cl → M:M+2 ≈ 3:1 · Br → ≈ 1:1 · I → mass 127 (and HI⁺ 128) · odd M⁺ → odd number of N · ¹³C isotope peak = M+1, ignore it · CDCl₃ solvent peak at 77.0, ignore it. H=1, C=12, N=14, O=16, Cl=35.5, Br=80.