Organic ChemistryCH. 25
Definitions• Organic means “based on carbon” • Hydrogen, oxygen, and other
elements are sometimes present• Inorganic means all those
compounds without carbon• Exceptions: Diamond, graphite,
carbon dioxide
What’s So Special About Carbon?
• It can form 4 covalent bonds• With other carbon atoms• With other elements• Forms long chains (straight or
branched)• Rings and hoops
Types of Carbon Atoms
• Primary carbon (1o)– a carbon bonded to one other carbon
• Secondary carbon (2o)– a carbon bonded to two other carbons
• Tertiary carbon (3o)– a carbon bonded to three other carbons
C
C
C
C
H
H
H
C C
H
HC
C
C
H
C
C
C
C
H
H
H
C C
H
HC
C
C
H
C
C
C
C
H
H
H
C C
H
HC
C
C
H
C
C
C
C
H
H
H
C C
H
HC
C
C
H
Some organic chemicals
DNA
Essential oils
Medicines•Active Pharmaceutical Ingredients•Excipients
Materials
Fuels
Pigments
Hydrocarbons
• Compounds which contain only carbon and hydrogen
• Obtained from petroleum distillation• Fuels, solvents, lubricants, waxes,
paving materials• Starting materials for countless other
products
Hydrocarbons- Types
• Aliphatic Long chains (can be branched)
• Alicyclic Rings or hoops
Aliphatic Hydrocarbons
• 2 Types
• Saturated (only single bonded carbons)
• Unsaturated (can contain double or triple bonded carbons)
Saturated Hydrocarbons:Alkanes
• All end in –ane• Only single bonds• Generic formula CnH(2n+2) • Known as a homologous series (add CH2
unit each time)– Methane CH4 (Natural Gas)– Propane C3H8 (common fuel gas)– Butane C4H10 (common fuel gas)– Gasoline (A mixture of liquid hydrocarbons
from heptane C7H16 to Decane C10H22
Alkanes
The First 10 “Normal” AlkanesName Formula M.P. B.P. # Structural Isomers
• Methane CH4 -183 -162 1
• Ethane C2H6 -172 -89 1
• Propane C3H8 -187 -42 1
• Butane C4H10 -138 0 2
• Pentane C5H12 -130 36 3
• Hexane C6H14 -95 68 5
• Heptane C7H16 -91 98 9
• Octane C8H18 -57 126 18
• Nonane C9H20 -54 151 35
• Decane C10H22 -30 174 75
C1 - C4 are Gases at Room Temperature
C5 - C16 are Liquids at Room Temperature
Prefixes for # of Carbons
1 Meth 6 Hex
2 Eth 7 Hept
3 Prop 8 Oct
4 But 9 Non
5 Pent 10 Dec
IUPAC Rules for Naming Branched Alkanes
– Find and name the parent chain in the hydrocarbon - this forms the root of the hydrocarbon name
– Number the carbon atoms in the parent chain starting at the end closest to the branching
– Name alkane branches by dropping the “ane” from the names and adding “yl”. A one-carbon branch is called “methyl”, a two-carbon branch is “ethyl”, etc…
– When there are more than one type of branch (ethyl and methyl, for example), they are named alphabetically
– Finally, use prefixes to indicate multiple branches
Branched- Chains
• Designate the location (number of the carbon on the parent chain) for each attached group
1 2 3 4 5
2-methyl
Some Simple Alkanes
• 2-methylpentane
• 3-ethylhexane
• 2,2-dimethylbutane
• 2,3-dimethylbutane
Example 1: 2,2-dimethylpentane
• The parent chain is indicated by the ROOT of the name - “pentane”. This means there are 5 carbons in the parent chain.
CH3
CH2CH2
CH2CH3
• “dimethyl” tells us that there are TWO methyl branches on the parent chain. A methyl branch is made of a single carbon atom.
• “2,2-” tell us that BOTH methyl branches are on the second carbon atom in the parent chain.
CH31
CCH23
CH2
4
CH35
CH3
CH3
1
2
3
4
5
Example 2: 3-ethyl-2,4-dimethylheptane• The parent chain is indicated
by the ROOT of the name - “heptane”. This means there are 7 carbons in the parent chain.
CH3
CH2CH2
CH2CH2
CH2CH3
• “2,4-dimethyl” tells us there are TWO methyl branches on the parent chain, at carbons #2 and #4.
• “3-ethyl-” tell us there is an ethyl branch (2-carbon branch) on carbon #3 of the parent chain.
1
2
3
4
5
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CH3
CHCH
CHCH2
CH2CH3
CH2CH3
CH3 CH3
Example 3: 2,3,3-trimethyl-4-propyloctane• The parent chain is indicated
by the ROOT of the name - “octane”. This means there are 8 carbons in the parent chain.
• “2,3,3-trimethyl” tells us there are THREE methyl branches - one on carbon #2 and two on carbon #3.
• “4-propyl-” tell us there is a propyl branch (3-carbon branch) on carbon #4 of the parent chain.
1
2
34
5
7
6
8
1
23
45
7
6
8
CHC
CHCH2
CH2
CH2CH3
CH3
CH3
CH3
CH3CH2
CH2
CH3
Example 4: Name the molecules shown!
• parent chain has 5 carbons - “pentane”
• two methyl branches - start counting from the right - #2 and #3
• 2,3-dimethylpentane
CH3
CH2
CHCH
CH3
CH3
CH3
• parent chain has 8 carbons - “octane”
• two methyl branches - start counting from the left - #3 and #4
• one ethyl branch - #5• name branches alphabetically3,4-dimethyl
43
octane
5
5-ethyl-
Isomers
• Straight chain alkanes: An alkane that has all its carbons connected in a row.• Branched chain alkanes: An alkane that has a branching connection of carbons.
Structural Isomerism
• Structural isomers are molecules with the same chemical formulas but different molecular structures - different “connectivity”.
• They arise because of the many ways to create branched hydrocarbons.
CH3
CH2CH2
CH2CH3
CH3
CH2CH
CH3
CH3
n-pentane, C5H12
2-methlbutane, C5H12
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Isomers• Isomers - organic molecules that have:
– Identical molecular formulas, but– Differing internal arrangement of atoms
•Different isomers are completely different compounds. They have different structures, different physical properties such as melting point and boiling point, and may have different physiological properties.
•Isomers: carbons in butane (C4H10) can be arranged in two ways; four carbons in a row (linear alkane) or a branching (branched alkane). These two structures are two isomers for butane.
Learning Check
• Draw all possible structural isomers of C5H12
Unsaturated HydrocarbonsAlkenes
• 1 Double Bond• Homologous Series remains the same, add
CH2 each time
• Generic formula CnH2n
• Ethene (C2H4) common name ethylene
• Butene (C4H8)
• 2 double bonds are called Dienes• 3 double bonds are called Trienes
Unsaturated HydrocarbonsAlkynes
• Contains a triple bond• Names end in -yne• Generic formula CnH(2n-2)
• Most Familiar example is ethyne• Common name acetylene C2H2
• Welding fuel kept dissolved in acetone
Naming Alkenes and Alkynes
When the carbon chain has 4 or more C atoms, number the chain to give the lowest number to the double or triple bond.
1 2 3 4
CH2=CHCH2CH3 1-butene
CH3CH=CHCH3 2-butene
CH3CCCH3 2-butyne
Naming Alkenes and Alkynes
When the carbon chain has 4 or more C atoms, number the chain to give the lowest number to the double or triple bond.
1 2 3 4
CH2=CHCH2CH3 1-butene
CH3CH=CHCH3 2-butene
CH3CCCH3 2-butyne
Alicyclic Hydrocarbons
• 2 types• Saturated rings
– Cyclohexane C6H12
• Aromatic rings– Benzene C6H6
Alkanes - Cycloalkanes• A cycloalkane is made of a hydrocarbon chain
that has been joined to make a “ring”.
CH3
CH2
CH3 CH2
CH2
CH2
n-propaneC3H8
cyclopropaneC3H6
60° bond angleunstable!!
109.5° bond angle
•Note that two hydrogen atoms were lost in forming the ring!•What is the general formula for a cycloalkane?
CycloalkanesCycloalkanes: An alkane that contains a ring of carbon atoms. Ring sizes from 3 carbons to 30 or higher are known.
Drawing and Naming Cycloalkanes
Cycloalkanes are represented by polygons. A triangle represents cyclopropane, a square represents cyclobutane, a pentagon represents cyclopentane, and so on.
•Line structure: A shorthand way of drawing structures in which atoms aren’t shown; instead a carbon atom is understood to be at each corner and hydrogens are “understood”.
•Step 1: Use the cycloalkane name as the parent chain.•Step 2: Number the substituents starting at the group that has alphabetical priority, and proceed around the ring in the direction that gives the second substituent the lower possible number.
Additional Rules for Naming Cyclics
Cycloalkanes with Side Groups
CH3
CH3
CH3
CH3
CH3
CH3
methylcyclopentane
1,2-dimethylcyclopentane
1,2,4-trimethylcyclohexane
Learning Check
Write the IUPAC name for each of the following unsaturated compounds:
A.CH3CH2CCCH3
CH3
B. CH3C=CHCH3 C.
CH3
Learning CheckCH3
CH3
CH3
CH3
CH3
Name those alkenes...
CH
CH
CH3 CH CH3
CH3
CH
CH
CH2
CH2
CH2
Br
cis-4-methyl-2-pentene2-methyl-2-hexene
cyclopentene
cis-3-heptene
trans-2-bromo-3-methyl-2-pentene
Cis and Trans Isomers
Double bond is fixed Cis/trans Isomers are possible
CH3 CH3 CH3
CH = CH CH = CH
cis trans CH3
Cis- and Trans- terminologyIf alkenes have two different substituents at each end
of the C=C then they can exist as stereoisomers because there is restricted rotation of the double bond.
• In cis isomers, two methyl groups are close together on the same side of the double bond.
• In trans isomer, two methyl groups are far apart on opposite side of the double bond.
• Both cis and trans isomers have the same formula and connections between the atoms but have different three dimensional structures because the way the groups are attached to the carbons.
• Cis-trans isomerism occurs in an alkene whenever each double bond carbon is bonded to two different substituent groups. Cis-trans isomerism is not possible if one of the double bond carbons is attached to two identical groups.
Name These
C CCH3
H
CH3
CH2CH3
C CCl
H
CH2
Cl
CH3
Aromatic Compounds and Benzene
Aromatic compounds contain benzene.
Benzene, C6H6 , is represented as a six carbon ring with 3 double bonds.
Two possible resonance structures can be drawn to show benzene in this form.
H
H
H
H
H
H
HH
H
H
H
H
• Experimental evidence suggest that all six carbon-carbon bonds in benzene are identical.
• The properties, including the above one, of benzene can only be explained by assuming that the actual structure of benzene is an average of the above two possible equivalent structures-known as resonance.
• Simple aromatic compounds like benzene are non-polar, insoluble in water, volatile, and flammable.
• Unlike alkenes, several aromatic hydrocarbons are toxic. Benzene itself is implicated as a cancer causing chemical.
Aromatic Compounds in Nature and Health
Many aromatic compounds are common in nature and in medicine.
COOH
COOCH3
CHO
OCH3
OH
Aspirin Vanillin
CHCOOH
CH3
CH3CHCH2
CH3
Ibuprofen
Naming Aromatic Compounds
Aromatic compounds are named with benzene as the parent chain. One side group is named in front of the name benzene. - No number is needed for mono-substituted benzene since
all the ring positions are identical.
methylbenzene chlorobenzene (toluene)
CH3 Cl
Naming Aromatic Compounds
When two groups are attached to benzene, the ring is numbered to give the lower numbers to the side groups. The prefixes ortho (1,2), meta (1,3-) and para (1,4-) are also used.
CH3
CH3
Cl
Cl
Cl
CH3
1,2-dimethylbenzene 1,3-dichlorobenzene 1-chloro-4-methylbenzene
(ortho-dimethylbenzene) (meta-dichlorobenzene) (para-chloromethylbenzene)
Some Common Names
Some substituted benzene rings also use a common name. Then naming with additional more side groups uses the ortho-, meta-, para- system.
CH3
Cl
CH3 OH
Toluene meta-chlorotoluene phenol(Methylbenzene) (meta-chloromethylbenzene) (hydroxybenzene)
• Many substituted aromatic compounds have common names in addition to their systematic names.
Learning Check
Select the names for each structure:
a. Chlorocyclohexaneb. Chlorobenzenec. 1-chlorobenzene
a. Meta-xyleneb. Meta-dimethylbenzenec. 1,3-dimethylbenzene
Cl
CH3
CH3
New Attached Groups
• Phenyl
• Benzyl
• Nitro -NO2
2,4,6-trinitrotoluene
Benzyl alcohol
4-phenyl-1-butene
Refer to your chart for order of priority!
Organic Chemistry:
Functional Groups
Origin of organic compounds
• Naturally occurring organic compounds are found in plants, animals, and fossil fuels
• All of these have a plant origin• All of these rely on the “fixing” of C from CO2
• Synthetic organic compounds are derived from fossil fuels or plant material
• Organic reactions often much slower than inorganic reactions–must break strong covalent bond–trying to find new catalysts to use
• Substitution Reactions- an atom (or group of atoms) replaces another atom or group of atoms
Substitution Reactions
• A halogen (shown as “X”) can replace a hydrogen to make a halocarbon:R-H + X2 R-X + HX
• Sunlight is often a sufficient catalyst:
CH4 + Cl2 → CH3Cl + HClUV light
SUBSTITUTIONSATURATED COMPOUNDS ONLY
ONE KIND OF ATOM OR GROUP IS SUBSTITUTED WITH ANOTHER KIND OF ATOM OR GROUP
PRODUCE HALIDES
C4H10 + Cl2 → C4H9Cl + HCl
TRY THESE!C3H8 + I2 → C3H7I + HI
C7H16 + F2 → C7H15F + HF
BE ABLE TO DRAW REACTANTS AND PRODUCTS
BE ABLE TO
NAME
PRODUCTS
Addition Reactions
• The carbon-carbon single bond is not easy to break
• In double bonded alkenes, it is easier to break a bond
• Addition reaction- substance is added at the double or triple bond location, after it is broken
Addition Reactions
• If a halogen is added in an addition reaction, the result is a halocarbon that is disubstituted - middle p. 734
• The addition of bromine is often used as a test for saturation - p.734
• Addition of a hydrogen halide? -called monosubstituted halocarbon
ADDITION RxnsADDING 2 OR MORE ATOMS TO CARBON ATOMS THAT ARE ATTACHED TO OTHER CARBON ATOMS BY DOUBLE OR TRIPLE BONDS.
OCCUR MORE EASILY THAN SUBSTITUTION
HOW HALIDES ARE MADE
ALKENES AND ALKYNES
C6H12 + Cl2 → C6H12Cl2
TRY THESE!!C7H14 + Br2 → C7H14Br2
C3H6 + I2 → C3H6I2
BE ABLE TO DRAW AND
NAME REACTANTS
AND PRODUCTS
POLYMERIZATION
CONDENSATION
• MONOMERS JOIN BY DEHYDRATION (DEHYDRATION SYNTHESIS).
• I.E. POLYESTERS, SILICONES, NYLONS, SOME PLASTICS
ADDITION• OPENING OF
DOUBLE AND TRIPLE BONDS TO JOIN MONOMERS.
• I.E. VINYL PLASTICS LIKE POLYETHELENE AND POLYSTYRENE.
LARGE MOLECULES(POLYMERS) ARE MADE FROM SMALLER MOLECULES CALLED MONOMERS.
CAN
BE
NAT
URA
L O
R SY
NTH
ETIC
PRO
TEIN
S, S
TARC
HES
,RU
BBER
NYL
ON
, PO
LYES
TER,
RU
BBER
D. Polymers • Polymers – large chainlike molecules made from many small molecules called
monomers – Simplest polymer – polyethylene– Polyethylene results from addition polymerization.
D. Polymers • Condensation polymerization – a small
molecule (often water) is released for each addition of a monomer to the polymer chain
• Copolymer – 2 different types of monomers combine to form the chain
– Nylon
Functional Groups• Most organic chemistry involves
substituents–often contain O, N, S, or P–also called “functional groups”-
they are the chemically functional part of the molecule, and are the non-hydrocarbon part
Functional Groups• Functional group - a specific
arrangement of atoms in an organic compound, that is capable of characteristic chemical reactions.–What is the best way to classify
organic compounds? By their functional groups.
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Functional Groups
• A functional group is an atom or a group of atoms with characteristic chemical and physical properties. It is the reactive part of the molecule.
• Most organic compounds have C—C and C—H bonds. However, many organic molecules possess other structural features:
Heteroatoms—atoms other than carbon or hydrogen. Bonds—the most common bonds occur in C—C and C
—O double bonds. These structural features distinguish one organic
molecule from another. They determine a molecule’s geometry, physical properties, and reactivity, and comprise what is called a functional group.
Introduction to Organic Molecules and Functional Groups
74
• Heteroatoms and bonds confer reactivity on a particular molecule.
Heteroatoms have lone pairs and create electron-deficient sites on carbon.
Bonds are easily broken in chemical reactions. A bond makes a molecule a base and a nucleophile.
Don’t think that the C—C and C—H bonds are unimportant. They form the carbon backbone or skeleton to which the functional group is attached.
75
Polar; some sugarsExample: Acetone
Polar, forms H-bonds; some sugarsand amino acids Example: EthanolR OH
R HCO
R RCO
R OHCO
R HN H
R SH
Biologically ImportantFunctional Groups
Thiols
AminesAmino
CarboxylicAcidsCarboxyl
Ketones
AldehydesCarbonyl
AlcoholsHydroxylCompoundStructureGroup Significance
Polar; some sugarsExample: Formaldehyde
Polar, acidic; fats and amino acidsExample: Acetic acid
Polar, basic; amino acidsExample: Tryptophan
Disulfide Bonds; some amino acidsExample: Ethanethiol
Polar, forms H-bonds; some sugarsand amino acids; Example: Ethanol
Polar; some sugarsExample: Formaldehyde
Polar; some sugarsExample: Acetone
Polar, acidic; fats and amino acidsExample: Acetic acidDisulfide Bonds; some amino acidsExample: Ethanethiol
Functional Groups
Functional Groups• The symbol “R” is used to
represent any carbon chains or rings
Alcohols
• Alcohols - a class of organic compounds with an -OH group–The -OH functional group in alcohols
is called a “hydroxyl” group; thus R-OH is the formula
• How is this different from the hydroxide ion? (covalent bonding with the carbon- not ionic with a metal like bases)
Alcohols• Aliphatic alcohols classified into
categories according to the number of R groups attached to the carbon with the hydroxyl–1 R group: primary alcohol–2 R groups: secondary alcohol–3 R groups: tertiary alcohol
Alcohols• Both IUPAC and common names• For IUPAC:
–drop the -e ending of the parent alkane name; add ending of -ol, number the position of -OH
–parent is the longest chain that contains the carbon with the hydroxyl attached.
Alcohols
• The hydroxyl is given the lowest position number
• Alcohols containing 2, 3, and 4 of the -OH substituents are named diols, triols, and tetrols respectively
Alcohols• Common names:
–similar to halocarbons, meaning name the alkyl group, then followed by the word alcohol
–One carbon alcohol = methyl alcohol
Alcohols
• More than one -OH substituents are called glycols (ethylene glycol?)
• Phenols - compounds in which a hydroxyl group is attached directly to an aromatic ring.
• Cresol is the common name of o, m, and p isomers of methylphenol
Properties of Alcohols
• Much like water, alcohols are capable of hydrogen bonding between molecules–this means they will boil at a higher
temp. than alkanes and halocarbons with a comparable number of atoms
Properties of Alcohols
• Alcohols are derivates of water; the -OH comes from water, and thus are somewhat soluble
• Alcohols of up to 4 carbons are soluble in water in all proportions; more than 4 carbons are usually less soluble, because the longer carbon chain is more nonpolar
Properties of Alcohols
• Many aliphatic alcohols used in laboratories, clinics, and industry–Isopropyl alcohol (2-propanol) is
rubbing alcohol; used as antiseptic, and a base for perfume, creams, lotions, and other cosmetics
• Ethylene glycol (1,2-ethanediol) - commonly sold as “antifreeze”
Properties of Alcohols
• Glycerol (1,2,3-propanetriol) - used as a moistening agent in cosmetics, foods, and drugs; also a component of fats and oils
• Ethyl alcohol (ethanol) used in the intoxicating beverages; also an important industrial solvent
Properties of Alcohols
• Denatured alcohol- means it has been made poisonous by the addition of other chemicals, often methyl alcohol (methanol, or wood alcohol).
• As little as 10 mL of methanol has been known to cause permanent blindness, and 30 ml has resulted in death!
Ethers
• A class of organic compounds in which oxygen is bonded to 2 carbon groups: R-O-R is formula
• Naming? The two R groups are alphabetized, and followed by ether
• Two R groups the same? Use the prefix di-
Ethers
• Diethyl ether is the one commonly called just “ether”–was the first reliable general
anesthetic–dangerous- highly flammable, also
causes nausea• ethers are fairly soluble in water
Aldehydes and Ketones• Review:
–alcohol has an oxygen bonded to a carbon group and a hydrogen
–ether has an oxygen bonded to two carbon groups
• An oxygen can also be bonded to a single carbon by a double bond
Aldehydes and Ketones
• The C=O group is called the “carbonyl group”– it is the functional group in both
aldehydes and ketones• Aldehydes - carbonyl group always
joined to at least one hydrogen (meaning it is always on the end!)
A. Aldehydes and Ketones – Aldehyde – carbonyl group always appears on the end of the
hydrocarbon chain and has at least one H atom bonded to the carbonyl group
Aldehydes and Ketones
• Ketones - the carbon of the carbonyl group is joined to two other carbons (meaning it is never on the end)
Aldehydes and Ketones• Naming?
–Aldehydes: identify longest chain containing the carbonyl group, then the -e ending replaced by -al, such as methanal, ethanal, etc.
Ketones: longest chain w/carbonyl, then new ending of -one; number it?
propanone, 2-pentanone, 3-pentanone
Aldehydes and Ketones
• Neither can form intermolecular hydrogen bonds, thus a much lower b.p. than corresponding alcohols
• wide variety have been isolated from plants and animals; possible fragrant odor or taste; many common names
Aldehydes and Ketones
• Benzaldehyde• Cinnamaldehyde• Vanillin• Methanal (the common name is:
formaldehyde)–40% in water is formalin, a
preservative
Aldehydes and Ketones
• Propanone (common: acetone) is a good solvent; miscible with water in all proportions
• why is it a good substance used in nail-polish removers? (a powerful solvent-able to dissolve both polar & nonpolar)
The Carboxylic Acids…
• Also have a carbonyl group (C=O), but is also attached to a hydroxyl group (-OH) = “carboxyl” group
• general formula: R-COOH–weak acids (ionize slightly)
• Named by replacing -e with -oic and followed by the word acid
• methanoic acid; ethanoic acid
Carboxylic Acids
• Abundant and widely distributed in nature, many having a Greek or Latin word describing their origin–acetic acid (ethanoic acid) from
acetum, meaning vinegar–many that were isolated from fats
are called fatty acids
C. Carboxylic Acids and Esters
The Esters…
• General formula: RCOOR• Derivatives of the carboxylic acids, in
which the -OH from the carboxyl group is replaced by an -OR from an alcohol:carboxylic acid + alcohol ester + water
• many esters have pleasant, fruity odors- banana, pineapple, perfumes
C. Carboxylic Acids and Esters
• Esters – a carboxylic acid reacts with an alcohol to form an ester and a water molecule
– General formula
C. Carboxylic Acids and Esters • To name esters
– Use the alkyl name from the alcohol followed by the acid name, where the –ic ending is replaced by –ate.
isopropylethanoate
Esters
• Although polar, they do not form hydrogen bonds (reason: there is no hydrogen bonded to a highly electronegative atom!)–thus, much lower b.p. than the
hydrogen-bonded carboxylic acids they came from
Esters
• Can be prepared from a carboxylic acid and an alcohol; usually a trace of mineral acid added as catalyst (because acids are dehydrating agents)
Esters
• Naming? It has 2 words:–1st: alkyl attached to single
bonded oxygen from alcohol–2nd: take the acid name, remove
the -ic acid, add -ate
Organic NomenclatureSuffixes/Meanings I
• -ane Alkane (saturated hydrocarbon)• -ene Alkene (one double bond) • -yne Alkyne (one triple bond)• -ine organic amine (amphetamine,
caffeine, cocaine, morphine, heroin)
• -one Ketone (acetone, nail polish remover)
Organic NomenclatureSuffixes/Meanings II
• -ase Enzymes ( protein catalysts in biochemical
reactions)
• -ose Sugars (glucose, sucrose)• -ol Alcohols• -al Aldehydes
(formaldehyde)• -ate Esters (many flavors and
fragrances)• -adeSomething to drink
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