Chemistry · Units 4 & 8 · Quick reference

Organic Chemistry

Grades 11–12+8 pages

Bonding and structure drawing, functional groups and IUPAC names, isomers and stereochemistry, acids and bases, resonance, curly-arrow mechanisms, alcohols, carbonyls and aromatic rings, IR, NMR and mass spectra, polymers and biomolecules.

1Bonding2Structures3Functional groups4IUPAC names5Isomers6R/S7E/Z8Acids & bases9Resonance10Curly arrows11SN1, SN212E1, E213Alkenes14Alcohols15Carbonyls16Aromaticity17IR181H NMR19Mass spec20Polymers21Biomolecules22Roadmap23Practice

1Bonding & Hybridizationcarbon makes four bonds

Why carbon

Carbon has 4 valence electrons and forms 4 covalent bonds: chains, branches and rings. Organic chemistry is the chemistry of carbon compounds. Wöhler made urea from an inorganic salt in 1828.

Count bonds in CH₂=CH–C≡N Worked

Draw every bond, H included
C=C: 1 σ + 1 π; C≡N: 1 σ + 2 π; plus 4 single bondsσ / π
6 σ, 3 π; carbons sp², sp², sp; N is spgroups

Formal charge

FC = V − (lone-pair e⁻) − ½(bonding e⁻)

Polar bonds

Electronegativity C 2.5, O 3.5: in C–O and C=O the oxygen is δ− and the carbon δ+. Electron-poor carbon is where nucleophiles attack (§10).

Count groups, read the hybrid
Groups on C	Hybrid	Shape, angle	Example
4	sp³	tetrahedral, 109.5°	ethane
3	sp²	trigonal planar, 120°	ethene
2	sp	linear, 180°	ethyne

Sigma and pi

Every single bond is one σ (end-on overlap).
A double bond is 1 σ + 1 π; a triple bond is 1 σ + 2 π.
π bonds block rotation and hold the reactive electrons.

Hybrids in ethanal, CH₃CHO Worked

CH₃ carbon: 4 groupssp³
C=O carbon: 3 groupssp²
O: C=O plus 2 lone pairssp²

Lone pairs count as groups
Atom in	Groups	Shape at atom
alcohol O (C–O–H)	4 (2 lone pairs)	bent, about 104.5°
amine N	4 (1 lone pair)	pyramidal, about 107°
carbonyl O (C=O)	3 (2 lone pairs)	sp², trigonal

Bond patterns to know
Atom	Neutral	−1	+1
C	4 bonds	3 bonds + 1 pair	3 bonds, no pair
N	3 bonds + 1 pair	2 bonds + 2 pairs	4 bonds
O	2 bonds + 2 pairs	1 bond + 3 pairs	3 bonds + 1 pair

Groups give the hybrid

Four groups: sp³. Three: sp². Two: sp. Count lone pairs as groups.

2Drawing StructuresLewis, condensed, skeletal

Propanal, two ways

Skeletal to formula Worked

(CH₃)₂CHCH₂CH₂OH
5 carbons, 1 O; fill each C to 4 bondscount
C₅H₁₂Oformula

Common slips

Five bonds to a carbon.
Leaving off the H on O or N.
Straight chains that hide carbons: draw zigzags.

Same molecule, four forms
Style	Propanal
Condensed	CH₃CH₂CHO
Molecular	C₃H₆O
Lewis	every bond and lone pair (O has 2 pairs)

Skeletal rules

Each line end and corner is a carbon.
Hydrogens on carbon are not drawn: add H until each C has 4 bonds.
Draw every heteroatom (O, N, halogen) and the H on it.
Draw chains as zigzags.

Degrees of unsaturation

DoU = (2C + 2 + N − H − X) ÷ 2

Condensed shorthand

(CH₃)₂CH– isopropyl; (CH₃)₃C– tert-butyl; –CHO aldehyde; –COOH acid; –COOR ester; –CN nitrile.

Condensed to skeletal

Reading a DoU Worked

C₆H₆: (14 − 6) ÷ 2 = 4ring + 3 C=C
C₆H₁₂O: (14 − 12) ÷ 2 = 1one C=O, C=C or ring
C₂H₅Br: halogen counts as H, DoU 0saturated

Corners are carbons

Every corner and end is C. Fill each carbon to four with hidden H.

Organic ChemistryChemistry · Units 4 & 8 · continued

3Functional Groupsthe reactive part

Hydrocarbons and singles
Group	Pattern	Name ending
alkene	C=C	-ene
alkyne	C≡C	-yne
haloalkane	C–X	halo- (prefix)
alcohol	C–OH	-ol

Oxygen and nitrogen
Group	Pattern	Name ending
ether	C–O–C	alkoxy- (prefix)
amine	C–NH₂	-amine
aldehyde	R–CHO	-al
ketone	R–CO–R	-one

Acid family
Group	Pattern	Name ending
carboxylic acid	R–COOH	-oic acid
ester	R–COO–R	-oate
amide	R–CONH₂	-amide
nitrile	R–C≡N	-nitrile

4IUPAC Namingparent, numbers, prefixes

Chain roots
C	Root	C	Root
1	meth-	6	hex-
2	eth-	7	hept-
3	prop-	8	oct-
4	but-	9	non-
5	pent-	10	dec-

Five steps

Parent: the longest chain that holds the main group (and C=C).
Number from the end that gives the main group the lowest locant.
Substituents (methyl, ethyl, chloro) get locants too.
Alphabetize prefixes; di-, tri- do not count.
Write: locants, prefixes, root, ending.

Each name checked against its structure

Ester names Worked

CH₃CH₂COOCH₂CH₃
alcohol part first (ethyl), acid part second (propanoate)two words
ethyl propanoatename

Name CH₃CH(OH)CH₂CH(CH₃)₂ Worked

Longest chain with C–OH: 5 C, pentan-…-olparent
Number from the OH end: OH on C2, methyl on C4lowest locant
4-methylpentan-2-olname

Main group wins the suffix
Priority	Suffix
carboxylic acid	-oic acid
ester	-oate
aldehyde	-al
ketone	-one
alcohol	-ol

Lowest numbers win

Number from the end nearer the main group; ties go to the first point of difference.

5Isomerssame formula, different molecule

Types of isomer
Kind	What differs	Example
Constitutional	which atoms connect	butane vs 2-methylpropane
Enantiomers	mirror images that cannot be stacked	(R)- vs (S)-butan-2-ol
Diastereomers	stereoisomers, not mirror images	(E)- vs (Z)-but-2-ene
Conformers	rotation about σ bonds	not isomers you can isolate

Three isomers of C₅H₁₂

Connect, then space

Different connections: constitutional. Same connections, different 3-D: stereo.

Functional-group isomers, C₂H₆O Worked

CH₃CH₂OH: an alcohol, H-bonds, a liquidethanol
CH₃OCH₃: an ether, no O–H, a gasmethoxymethane
same formula, different groups and propertiesconstitutional

History

Wöhler and Liebig found two compounds with the same formula but different structures: isomers.

Organic ChemistryChemistry · Units 4 & 8 · continued

6Chirality & R/Shandedness at carbon

Wedge: toward you. Dashes: away.

Vocabulary
Term	Meaning
Enantiomers	mirror images; same properties except rotating light (equal, opposite)
Racemic mixture	50:50 R and S; no net rotation
Meso	has stereocenters but an internal mirror plane; not chiral
Count	n stereocenters: at most 2ⁿ stereoisomers

Spotting a stereocenter

An sp³ carbon with four different groups.
CH₂, CH₃ and C=C carbons are never stereocenters.
A molecule with one stereocenter is chiral.

Butan-2-ol, wedge drawing Worked

OH > CH₂CH₃ > CH₃ > Hrank by atomic number, then the next atoms
H points back; 1 → 2 → 3 runs clockwisetrace
Ranswer

Fischer projections

Horizontal lines come toward you, vertical lines go back. Sugars and amino acids are often drawn this way (D, L).

Assigning R or S

Rank the four groups by atomic number at the first point of difference (CIP rules).
Put the lowest (often H) pointing away.
Trace 1 → 2 → 3: clockwise is R, counterclockwise is S.
If the lowest group points toward you, reverse the answer.

Life is one-handed

Natural amino acids are the L form; L-alanine is (S). Tartaric acid has 2 stereocenters but only 3 stereoisomers, because one is meso.

Hand on the wheel

H in back, steer 1 to 2 to 3: turning right is R.

7Alkenes: E/Zno rotation about C=C

E or Z

On each alkene carbon, rank the two groups (CIP).
Higher groups on the same side: Z (zusammen, together).
Opposite sides: E (entgegen, opposite).
If one alkene carbon has two identical groups, there is no E/Z.

ClBrC=CHCH₃, Cl trans to CH₃ Worked

C1: Br > Cl; C2: CH₃ > Hrank
Br and CH₃ on the same sidecompare
(Z)-1-bromo-1-chloroprop-1-enename

Name CH₃CH=C(CH₃)CH₂CH₃ Worked

C2: CH₃ > H; C3: CH₂CH₃ > CH₃rank each end
CH₃ (on C2) and CH₂CH₃ opposite, as drawncompare
(E)-3-methylpent-2-enename

Cis is not always Z

Cis/trans compares like groups; E/Z compares ranks. In the example Cl is trans to CH₃, yet the alkene is Z.

Rings

Rings block rotation too: cis-1,2-dimethylcyclohexane has both CH₃ on one face; trans has one up, one down.

8Acids & BasespKa: lower is stronger

Brønsted–Lowry (1923)

An acid is a proton donor; a base is a proton acceptor. pKa = −log Ka: each pKa unit is a factor of 10.

Typical pKa values
Acid	pKa	Acid	pKa
HCl	−7	ethanol	16
acetic acid	4.76	acetone (α-H)	19
NH₄⁺	9.25	ethyne	25
phenol	10	ammonia	38
water	14	ethane	50

Stable base, strong acid

The more stable the conjugate base, the stronger the acid.

Why one acid is stronger: ARIO

Atom: across a row, more electronegative is more acidic (C–H < N–H < O–H); down a group, larger is more acidic.
Resonance: a delocalized conjugate base is stable (acetate).
Induction: nearby electronegative atoms pull charge away.
Orbital: more s character holds the pair closer (sp > sp² > sp³).

Induction in action Worked

CH₃COOH 4.76 → ClCH₂COOH 2.86 → CF₃COOH 0.23more pull, lower pKa

each F or Cl spreads the negative charge of the anionwhy

Which way does it go? Worked

CH₃COOH + NH₃ ⇌ CH₃COO⁻ + NH₄⁺
pKa 4.76 on the left, 9.25 on the rightcompare acids
equilibrium favors the weaker acid: goes rightanswer

Phenol vs ethanol Worked

phenoxide spreads its − charge into the ringresonance
ethoxide holds it on one Ono resonance
phenol (10) is about 1,000,000 times more acidic than ethanol (16)pKa

Size of the gap

Ka of acetic acid ≈ 1.7 × 10⁻⁵. Acetic acid (4.76) is about 100,000 times stronger than phenol (10).

Organic ChemistryChemistry · Units 4 & 8 · continued

9Resonanceelectrons spread, atoms stay

Form 1 ↔ form 2: the real ion is their average

Rules

Move electrons only (π bonds and lone pairs); never move atoms or break σ bonds.
Keep the same total charge and the octet on C, N, O.
Join forms with a double-headed arrow ↔, not ⇌.
The real molecule is a hybrid; it does not flip between forms.

Ranking contributors
Better form has	Why
more full octets	stability first
fewer charges	less separation
− on the more electronegative atom	O holds − better than C

Why acetate is stable Worked

the −1 charge is shared by two O atomstwo equal forms
both C–O bonds are the same length, between single and doubleevidence
stable base: acetic acid is a far stronger acid than ethanolpKa 4.76 vs 16

Where to look for resonance
Pattern	Example
lone pair next to a π bond	acetate, amide
+ charge next to a π bond	allyl cation
π bond in a ring of p orbitals	benzene
π bond to a more electronegative atom	C=O ↔ C⁺–O⁻

Benzene

6 π electrons spread evenly over 6 carbons; every C–C bond is the same length (§16).

Arrows move pairs

In resonance, only electrons move. If an atom moves, it is a different molecule.

10Curly Arrowsfollow the electron pairs

Arrow rules

An arrow shows a pair of electrons moving; a fishhook (half head) moves one.
Start at a lone pair or a bond; end at an atom or a new bond position.
Electrons flow from electron-rich to electron-poor.
Check charges and octets after every step.

Good leaving groups are weak bases
Leaving group	Quality
I⁻, Br⁻, TsO⁻, H₂O	good (weak bases)
Cl⁻	fair
OH⁻, OR⁻, NH₂⁻	poor: protonate OH first

Energy (up) against reaction progress

Alkyl groups donate electrons
Carbocation	Stability
3° (R₃C⁺)	most stable
2° (R₂CH⁺)	moderate
1° (RCH₂⁺)	poor
CH₃⁺	least

Reading the diagram

Each hump is a transition state (‡); a dip between humps is an intermediate. The highest hump sets the rate.

Who attacks whom
Nucleophile (Nu)	Electrophile (E)
electron-rich: lone pair, π bond, − charge	electron-poor: δ+, + charge, empty orbital
OH⁻, CN⁻, NH₃, H₂O, Br⁻, C=C	C–X carbon, C=O carbon, H⁺, carbocations

Rich to poor

Arrows run from the electron-rich tail to the electron-poor head.

11Substitution: SN2 & SN1Nu replaces a leaving group

SN2: bond forms as bond breaks

SN2

One step; rate = k[RX][Nu]: both in the rate law.
Backside attack: inversion of configuration.
Fastest at CH₃ and 1° carbons; blocked at 3°.
Strong nucleophile; polar aprotic solvent (acetone, DMSO).

Nucleophiles by strength
Nucleophile	Strength
HS⁻, CN⁻, I⁻, OH⁻, RO⁻	strong
Br⁻, NH₃, Cl⁻	fair
H₂O, ROH	weak

(S)-2-bromobutane + OH⁻ (SN2) Worked

2° carbon, strong Nu, one stepmechanism
OH enters opposite Br: geometry invertsinversion
(R)-butan-2-olproduct

Watch the substrate

Vinyl and aryl halides (Br on C=C or a ring) do not do SN1 or SN2.
Neopentyl carbons are too crowded for SN2.

SN1

Two steps: the leaving group leaves, then Nu adds to the carbocation.
Rate = k[RX]: only the substrate.
Best at 3°; flat cation gives a mix of R and S (racemic).
Weak nucleophile, polar protic solvent (water, alcohol).

(CH₃)₃CBr in water (SN1) Worked

3° carbon, weak Nu
Br⁻ leaves: (CH₃)₃C⁺slow step
water adds, loses H⁺: 2-methylpropan-2-olproduct

Organic ChemistryChemistry · Units 4 & 8 · continued

12Elimination & ChoosingE2, E1, and which wins

E2: base, C–H and C–Br act together

2-bromobutane + strong base, heat Worked

remove H from C1 or C3two choices
but-2-ene (disubstituted) vs but-1-enecompare
but-2-ene major (Zaitsev)product

E2 and E1

E2: one step, strong base; H and leaving group anti; rate = k[RX][B].
E1: carbocation first (like SN1), then loss of H⁺; rate = k[RX].
Zaitsev: the more substituted alkene is the major product.
Heat favors elimination over substitution.

Quick decision guide
Substrate	Strong Nu, weak base	Strong bulky base	Weak Nu, heat
1°	SN2	E2	slow
2°	SN2	E2	SN1 / E1
3°	SN1	E2	SN1 / E1

SN1, SN2, E1, E2 side by side
	SN2	SN1	E2	E1
Steps	1	2	1	2
Rate law	[RX][Nu]	[RX]	[RX][B]	[RX]
Substrate	1°, CH₃	3°	3°, 2°	3°
Reagent	strong Nu	weak Nu	strong base	weak base
Stereo	inversion	racemic	anti H, X	mix

Strong or weak first

Strong reagent: one step (SN2, E2). Weak reagent: cation first (SN1, E1).

13Addition to Alkenesthe π bond attacks

Propene + HBr: through the more stable cation

Cyclohexene + Br₂ Worked

Br₂ forms a 3-membered bromonium ionstep 1
Br⁻ attacks from the back facestep 2
trans-1,2-dibromocyclohexane (anti addition)product

Markovnikov’s rule

H adds to the alkene carbon that already has more H; the other group goes to the carbon that forms the more stable cation.

Common additions
Reagent	Adds	Product from propene
HBr	H, Br (Markovnikov)	2-bromopropane
H₂O, H⁺	H, OH (Markovnikov)	propan-2-ol
Br₂	Br, Br (anti)	1,2-dibromopropane
H₂, Pt	H, H (syn)	propane
BH₃ then H₂O₂, OH⁻	H, OH (anti-Markovnikov)	propan-1-ol

Why the 2° cation Worked

H⁺ on C1 gives CH₃–C⁺H–CH₃ (2°)path A
H⁺ on C2 gives ⁺CH₂–CH₂–CH₃ (1°)path B
2° is more stable, so Br bonds to C2answer

More alkyl groups, more stable
Alkene	Stability
tetrasubstituted R₂C=CR₂	most stable
trisubstituted	↓
disubstituted (trans > cis)	↓
monosubstituted RCH=CH₂	least

H joins the H-rich carbon

The alkene carbon with more H gets the new H (Markovnikov).

14Alcoholsthe O–H group

Classify, then predict
Class	C bearing OH has	Oxidized (Cr(VI) or PCC)
methanol	no C neighbor	methanal, then methanoic acid
1°	one C neighbor	aldehyde (PCC); acid (Cr(VI), H⁺)
2°	two C neighbors	ketone
3°	three C neighbors	no reaction

Butan-1-ol, butan-2-ol, 2-methylpropan-2-ol

Same mass, different boiling point Worked

ethanol, methoxymethane: both 46.1 g/mol
ethanol 78 °C; methoxymethane −25 °C; propane (44.1) −42 °Cbp
only ethanol has O–H: hydrogen bonds hold its molecules togetherwhy

Oxidation ladder Worked

ethanol → ethanal → ethanoic acid1°
butan-2-ol → butan-2-one, then stops2°
each step loses 2 H or gains 1 Opattern

Key reactions
Reaction	Reagent	Product
oxidation 1°	PCC	aldehyde
dehydration	H₂SO₄, heat	alkene (E1, Zaitsev)
to alkyl halide	HBr	R–Br (via R–OH₂⁺)
as acid	Na	alkoxide RO⁻ + H₂

Count C on the C–OH

One neighbor: 1°. Two: 2°. Three: 3° (will not oxidize).

Phenols

An OH on a benzene ring is a phenol, not an alcohol: it is far more acidic (pKa 10) and does not oxidize like a 1° or 2° alcohol.

Organic ChemistryChemistry · Units 4 & 8 · continued

15Carbonyl Chemistrythe C=O group

Nucleophilic addition to C=O

Acyl substitution: add, then kick out
Derivative	Leaving group	Reactivity
acid chloride	Cl⁻	highest
anhydride	RCOO⁻	high
ester	RO⁻	moderate
amide	NH₂⁻	lowest

Keto–enol

Propanone ⇌ prop-1-en-2-ol (keto form dominates). An α-H is weakly acidic (pKa 19) because the enolate is resonance-stabilized.

Aldehydes and ketones

C=O is polar: C δ+, O δ−; the flat sp² carbon is open to attack from either face.
Nu adds to C; O⁻ picks up H⁺. The carbon becomes sp³.
Aldehydes react faster than ketones (less crowded, more δ+).

Fischer esterification Worked

CH₃COOH + CH₃CH₂OH ⇌ CH₃COOCH₂CH₃ + H₂Oacid catalyst
ethyl ethanoate, 88.11 g/mol: fruity smellester
reverse it with water and acid or base: hydrolysisreverse

Additions to C=O
Reagent	With a ketone gives
NaBH₄ or LiAlH₄, then H⁺	2° alcohol (aldehyde: 1°)
R–MgBr (Grignard), then H₃O⁺	new C–C bond; 3° alcohol
HCN	cyanohydrin

Build propan-2-ol Worked

CH₃MgBr + ethanal (CH₃CHO)Nu: CH₃⁻ adds to C=O
then H₃O⁺O⁻ → OH
(CH₃)₂CHOH, propan-2-olproduct

Nucleophiles love δ+

Nucleophiles hit the C of C=O; the O takes the electrons.

16Aromaticityextra-stable rings

Each has 6 π electrons

Substitution keeps the ring
Reaction	Reagents	Product
nitration	HNO₃, H₂SO₄	nitrobenzene
bromination	Br₂, FeBr₃	bromobenzene
Friedel–Crafts	RCl, AlCl₃	alkylbenzene

Two more than four

Aromatic rings hold 4n + 2 π electrons: 2, 6, 10.

Hückel’s rule

Cyclic, planar and fully conjugated (a p orbital on every ring atom).
4n + 2 π electrons: 2, 6, 10 … is aromatic.
4n π electrons in a flat ring: antiaromatic (unstable).
Fails the shape test: nonaromatic.

Second substituent
Group on ring	Directs to
–OH, –NH₂, –CH₃ (activate)	ortho, para
–F, –Cl, –Br (deactivate)	ortho, para
–NO₂, –CN, –C=O (deactivate)	meta

Test the rule
Ring	π e⁻	Verdict
benzene	6	aromatic
pyrrole (N lone pair counts)	6	aromatic
cyclopentadienyl anion	6	aromatic
cyclobutadiene	4	antiaromatic
cyclooctatetraene (tub shape)	8	nonaromatic

Rings that fail

Cyclohexane: no π electrons.
Cyclooctatetraene: 8 π e⁻ and a tub shape, so it is not flat: nonaromatic.

17IR Spectroscopybonds absorb by type

Key bands, in cm⁻¹

Three zones

X–H above 2500; triple bonds 2100–2260; C=O 1665–1760.

Band table
Bond	cm⁻¹	Look
O–H alcohol	3200–3550	broad, strong
O–H acid	2500–3300	very broad
N–H	3300–3500	medium
C–H sp³	2850–2960	just below 3000
C–H sp², sp	3000–3300	just above 3000
C≡N, C≡C	2100–2260	sharp
C=O	1665–1760	strong, sharp
C=C	1620–1680	medium

Fingerprint

Below 1500 cm⁻¹ the pattern is unique to each compound; use it to match, not to assign.

C₃H₆O: strong 1715, nothing above 3000 Worked

strong 1715: C=Ocarbonyl
no broad O–H; no aldehyde C–H pairrule out
propanone (a ketone)answer

Alcohol, acid, ketone or ester?
Bands seen	Points to
broad 3300 only	alcohol
very broad 2500–3300 + 1710	carboxylic acid
1715, no O–H	ketone
1740, no O–H	ester

Organic ChemistryChemistry · Units 4 & 8 · continued

18¹H NMRenvironments, area, splitting

Chemical shift δ (ppm); TMS = 0

Ethyl ethanoate, CH₃COOCH₂CH₃ Worked

δ 2.0, 3H, singlet: CH₃–C=O (no H neighbors)signal 1
δ 4.1, 2H, quartet: O–CH₂, next to CH₃signal 2
δ 1.2, 3H, triplet: CH₃, next to CH₂signal 3

Read four things
Feature	Tells you
Number of signals	different H environments
Shift δ	neighbors: O, C=O, rings pull downfield
Integration	ratio of H in each signal
Splitting	n neighboring H give n + 1 peaks

O–H and N–H

Usually a broad singlet that does not split its neighbors (it exchanges); ethanol shows singlet, quartet, triplet.

¹³C NMR

One peak per carbon environment, no splitting: ethanol 2, ethyl ethanoate 4, benzene 1. C=O carbons sit far downfield.

Patterns to recognize
Group	Pattern
ethyl, –CH₂CH₃	2H quartet + 3H triplet
isopropyl, –CH(CH₃)₂	1H septet + 6H doublet
tert-butyl, –C(CH₃)₃	9H singlet
methyl ester, –COOCH₃	3H singlet

C₃H₆O: one singlet, 6H Worked

propanal would give 3 signalsrule out
two identical CH₃ next to C=Osymmetry
propanone; its ¹³C shows 2 signalsanswer

Neighbors plus one

Count H on the next carbons, add one: that many peaks.

19Mass Spectrometryweigh the ion

Computed M and M+2 peaks

Bromoethane Worked

peaks at 108 and 110, nearly equalM, M+2
equal pair: one Brisotopes
108 − 79 = 29: C₂H₅rest

History

Aston’s mass spectrograph (1919) split chlorine into masses 35 and 37. Bromine is about 51% bromine-79 and 49% bromine-81.

Reading a spectrum

M⁺, the molecular ion, gives the molar mass (lightest isotopes).
Cl: M and M+2 about 3 : 1. Br: about 1 : 1.
M+1 is about 1.1% per carbon (carbon-13).
Nitrogen rule: an odd M⁺ means an odd number of N (propan-1-amine, 59).

Common fragments
m/z	Ion	Hint
M − 15	lost CH₃	methyl branch
29	C₂H₅⁺	ethyl
43	CH₃CO⁺	methyl ketone
77	C₆H₅⁺	phenyl
91	C₇H₇⁺	benzyl

Isotope and mass clues
Clue	Means
M+2 ≈ ⅓ of M	one Cl
M+2 ≈ M	one Br
M+2 ≈ 4.5% of M	one S
odd M⁺	odd number of N

Peaks at 78 and 80, about 3 : 1 Worked

M+2 a third as tall: one Clisotopes
78 − 35 = 43: C₃H₇rest
C₃H₇Cl, e.g. 2-chloropropaneanswer

Honest weights

“A just weight and balance are the LORD’s: all the weights of the bag are his work” (Proverbs 16:11, KJV).

20Polymersmany small units joined

Addition-polymer monomers

Two ways to build

Addition: the π bond of each alkene opens; no atoms are lost; repeat unit –[CH₂–CHX]–.
Condensation: two functional groups join and give off a small molecule (H₂O).

Addition polymers: C=C opens
Monomer	Polymer	Use
ethene	polyethylene	bags, bottles
chloroethene	PVC	pipes
ethenylbenzene (styrene)	polystyrene	foam cups
tetrafluoroethene	PTFE	nonstick coating

Size

Polyethylene of 1,000 ethene units has a molar mass near 28,000 g/mol. PET (bottles) joins benzene-1,4-dicarboxylic acid and ethane-1,2-diol by ester links.

Condensation polymers
Polymer	Link	Lost
nylon-6,6	amide	H₂O
PET (polyester)	ester	H₂O
protein	peptide (amide)	H₂O
starch, cellulose	glycosidic	H₂O

Nylon-6,6 Worked

hexanedioic acid + hexane-1,6-diaminemonomers
–COOH + H₂N– → –CO–NH– + H₂Oamide link
repeat; the same bond as in proteinspolyamide

Organic ChemistryChemistry · Units 4 & 8 · continued

21Biomoleculesorganic chemistry of life

Functional groups in the molecules of life
Molecule	Groups it carries
glucose	–OH ×5, aldehyde (open chain) or ring hemiacetal
amino acid	–NH₂, –COOH, side chain R
fat	ester ×3, long C chains
DNA, RNA	phosphate esters, nitrogen bases (amines, amides)

Ring and chain

Open-chain glucose has 4 stereocenters; closing the ring at C1 adds a fifth, giving α and β forms.

Four families
Family	Monomer	Link
carbohydrate	glucose, C₆H₁₂O₆	glycosidic (ether)
protein	20 amino acids	peptide (amide)
lipid (fat)	glycerol + 3 fatty acids	ester
nucleic acid	nucleotide	phosphate ester

Dehydration synthesis Worked

2 C₆H₁₂O₆ → C₁₂H₂₂O₁₁ + H₂Omaltose
glycine + alanine → Gly-Ala + H₂Opeptide bond
hydrolysis adds the water backdigestion

Stereo in life

Cells build with D-sugars and L-amino acids only. Glucose, 180.16 g/mol, has 5 stereocenters in its ring form.

Saturated or not

Saturated fatty acids have only C–C single bonds and pack tightly (solid fats); a cis C=C makes a kink, so oils stay liquid.

Classic lab tests
Test	Positive for
iodine turns blue-black	starch
Benedict’s, heat: brick red	reducing sugar (glucose)
biuret turns violet	protein (peptide bonds)
translucent spot on paper	fat

22Reaction Roadmapfrom one group to another

Alkenes and halides
From	Reagent	To
alkene	H₂O, H⁺	alcohol (Markovnikov)
alkene	HBr	alkyl bromide
alkyl halide	OH⁻ (SN2 or SN1)	alcohol
alkyl halide	strong base, heat (E2)	alkene

Plan: propene to propanone Worked

propene + H₂O, H⁺ → propan-2-olMarkovnikov

propan-2-ol + Cr(VI) → propanone2° to ketone

Alcohols up the ladder
From	Reagent	To
alcohol	H₂SO₄, heat	alkene
1° alcohol	PCC	aldehyde
2° alcohol	Cr(VI), H⁺	ketone
aldehyde	Cr(VI), H⁺	carboxylic acid

Carbonyls
From	Reagent	To
ketone	NaBH₄, then H⁺	2° alcohol
acid + alcohol	H⁺, heat	ester
ester	H₂O with H⁺ or OH⁻	acid + alcohol
acid chloride	NH₃	amide

Plan: bromoethane to ethyl ethanoate Worked

CH₃CH₂Br + OH⁻ → ethanolSN2

ethanol + ethanoic acid, H⁺ → ethyl ethanoateesterify

Work backward

Start from the target; ask which group it came from one step before.

Count carbons

If the product has more carbons than the start, you need a C–C bond: a Grignard reagent on C=O (§15) is the classic choice.

23Practiceanswers on the right

Structure and reactions
Question	Answer
Hybridization of each C in CH₃CH=CH₂?	sp³, sp², sp²
Hybridization of N in CH₃C≡N?	sp
Name CH₃CH₂CH(CH₃)CH₂CH₂OH.	3-methylpentan-1-ol
DoU of C₅H₈?	2: two π bonds, or a ring + π
Stereocenters in 3-methylhexane?	1 (C3)
2-methylpropene + HBr gives?	2-bromo-2-methylpropane (via 3° cation)
More acidic: ethanol or acetic acid?	acetic acid (4.76 vs 16): resonance

Mechanisms and spectra
Question	Answer
(CH₃)₃CBr + H₂O, warm: which mechanism?	SN1 (3°, weak Nu)
CH₃Br + OH⁻: which mechanism?	SN2 (methyl, strong Nu)
C₃H₆O, IR 1715, one ¹H singlet?	propanone
M⁺ at 59 with no Cl or Br pattern?	odd: one N (e.g. propan-1-amine)
Is cyclobutadiene aromatic?	no: 4 π e⁻, antiaromatic
¹H NMR of CH₃CH₂Br?	2H quartet, 3H triplet
IR 1740, no O–H?	ester
Br₂ + cyclohexene: syn or anti?	anti (bromonium ion)

Quick checks
Question	Answer
Is L-alanine R or S?	S
¹H NMR signals in ethanol?	3 (triplet, quartet, singlet)
Butan-2-ol + H₂SO₄, heat: major product?	but-2-ene (Zaitsev)
Propan-1-ol + PCC?	propanal
Peaks at M and M+2, equal height?	one Br

Stretch
Question	Answer
DoU of C₆H₁₀: name one structure.	2: cyclohexene
Is pyridine aromatic?	yes: 6 π e⁻, flat ring
Ethanol → ethanoic acid needs?	Cr(VI), H⁺ (oxidation)