Carboxylic acids
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1 C: formic acid, methanoic acid 2 C’s: acetic acid, ethanoic acid PowerPoint PPT Presentation

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Carboxylic acids. 1 C: formic acid, methanoic acid 2 C’s: acetic acid, ethanoic acid 3 C’s: propionic acid, propanoic acid 4 C’s: butyric acid, butanoic acid. Aspirin : Should you take a daily dose?. (Prostaglandins F 2 a ).

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1 C: formic acid, methanoic acid 2 C’s: acetic acid, ethanoic acid

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Carboxylic acids

  • 1 C: formic acid, methanoic acid

  • 2 C’s: acetic acid, ethanoic acid

  • 3 C’s: propionic acid, propanoic acid

  • 4 C’s: butyric acid, butanoic acid

Aspirin : Should you take a daily dose?

(Prostaglandins F2a)

Prostaglandins are involved in the regulation of a variety of physiological

phenomena, including inflammation, blood clotting, and the induction of labor. Aspirin act by blocking the biosynthesis of prostaglandins in the cell.


Carboxylic Acid

Carboxylate ion

Electron-withdrawing groups stabilize a conjugate base,

making a carboxylic acid more acidic.

Electron-donating groups destabilize a conjugate base,

making a carboxylic acid less acidic.

Alpha Hydroxy Acids in Cosmetics

Carboxylic acids’ Derivatives


Preparing Biodiesel

Preparing Soaps


(cell wall transamidase)

NH3 + H2O NH4+ + OH-


RNH2, ArNH2 Primary, 1o Amines

R2NH, Ar2NH Secondary, 2oAmines

R3N, Ar3N Tertiary, 3o Amines





NaNO2 inhibits the growth of Clostridium botulinum.

Quote of The Day

Think like a wise man

but express yourself like

an ordinary one.




is the study of the three-dimensional structure of molecules.


Isomers : Different compounds that have the same

molecular formula.

Stereoisomers : Isomers that have the same bonding sequence

but differ in the orientation of their atoms in space.

  • Late 50’s, thalidomide was prescribed as an analgesic for morning sickness and used extensively in Europe and Canada despite strong warning that it not be used by pregnant women.

  • By 1961, it was recognized as the cause for numerous birth defects (~7-10,000 in 28 countries).


180° rotation

คู่ enantiomers

  • Each enantiomer of a stereoisomeric pair is optically active and has an equal but opposite-in-sign specific rotation.

  • One enantiomer will rotate polarized light in a clockwise direction, termed dextrorotatory (+), and its mirror-image partner in a counter-clockwise manner, termed levorotatory (–).

  • It is common practice to convert the observed rotation, α, to a specific rotation, [α].

  • Although two enantiomers have identical boiling points and melting points, they rotate the plane of polarized light in opposite directions. A polarimeter is used to measure the optical rotations of enantiomers.


Specific rotation, [a] = amount (degrees) that a substance rotates plane polarized light expressed in a standard form.

Carvone from caraway:   [α]D = +62.5º

Carvone from spearmint:   [α]D = –62.5º

Lactic acid from muscle tissue:   [α]D = +2.5º

Lactic acid from sour milk:   [α]D = –2.5º

How can one identify enantiomerism?

All objects may be classified with respect to chirality (from the Greek cheir = hand):

Chiral = Objects that are different from theirs mirror image;

i.e. golf clubs, scissors; enantiomers are chiral.

Achiral = Objects that are identical with theirs mirror image;

i.e. a pencil, a T-shirt.

Chiral molecule : (R)-lactic acid

Achiral molecule : water

Water (H2O)

  • Achiral molecules have either one or both of the following:

  • Plane of symmetry

  • Center of symmetry

Chiral molecules have chiral center (or stereo or stereogenic center):

an atom attached to 4 different atoms or groups.

(chiral carbon)

Designating the Configuration of Stereogenic Centers

The CIP system of nomenclature.

(R. S. Cahn, C. K. Ingold and V. Prelog)

  • Each stereogenic center in a molecule is assigned a prefix (R or S), according to whether its configuration is right- or left-handed.

  • The symbol R comes from the Latin rectus for right, and S from the Latin sinister for left.

The assignment of the prefixes depends on the

application of two rules:

The Sequence Rule

The Viewing Rule



The Sequence Rule

  • Assign sequence priorities to the four substituents by looking at the atoms attached directly to the chiral stereogenic carbon atom.

  • The higher the atomic number of the immediate substituent atom, the higher the priority; H–  <  C–  <  N–  <  O–  <  Cl–.

  • If two substituents have the same immediate substituent atom, evaluate atoms progressively further away from the chiral center until a difference is found. i.e. CH3–  <  C2H5–  <  ClCH2–  <  BrCH2–  <  CH3O–.

  • If double or triple bonded groups are encountered as

    substituents, they are treated as an equivalent set of single-

    bonded atoms. i.e. C2H5–  <  CH2=CH–  <  HC≡C–

The Viewing Rule

  • The chiral center must be viewed from the side opposite the lowest priority group.

  • Numbering the substituent groups from 1 to 4, with 1 being the highest and 4 the lowest in priority sequence, and put a viewers eye on the side opposite substituent #4.

  • If the progression from 1 to 3is clockwise, the configuration at the stereocenter is R. Conversely the counterclockwised progression is assigned as S.

Assign Priorities

Twist the lowest

priority to the


Rotate Priorities



View &



If you have troubles looking at the stereocenter, try Fischer Projections.

Only two kinds of motions are allowed for Fischer projection.

1) Rotation on page 180˚ is allowed for Fischer projection.

2) One group can be held steady while the other three rotate in either

a clockwise or a clockwise direction.

Assigning R, S configurations to Fischer projections.

  • Assign priorities to the four substituents in the usual way.

  • Perform one of the two allowed motions to place the group

    of lowest (4th) priority at the top or bottom of the Fischer

    projection if it is necessary.

  • Determine the direction of rotation in going from priority

    1 to 2 to 3, and assign R (clockwise) or

    S (counterclockwise).

Compounds Having Two or More Stereogenic Centers

Stereocenter 2

Stereocenter 1


(1R), (2S)-(-)-Ephedrine

(+)-Pseudoephedrine and (-)-Pseudoephedrine are diastereomers of (+)-Ephedrine.


  • Stereoisomers that are not mirror images of each other.

  • Diastereomers have similar chemical properties.

  • Diastereomers have different physical properties:

    melting points, boiling points, solubities in solvent, etc.

  • Diastereomers can be separated by fractional distillation,

    or crystallization.



Enantiomers: non-superimposable (different) mirror images; most of chemical and physical properties are identical.

Diastereomers: are stereoisomers that are not mirror images (all stereoisomers except enantiomers) and have different chemical and physical properties.

Relationships Between Stereoisomers


Enantiomeric with

Diastereomeric with

(1R), (2S)-(-)-Ephedrine

(1S), (2R)-(+)-Ephedrine

(1S), (2S)-(+)-



(1R), (2R)-(-)-


Cahn-Ingold-Prelog R/S notation = Specifies absolute configuration of a chiral center;

there is no correspondence between R and + or S and –

Meso Isomer:

an achiral molecule with 2 or more chiral centers and

an internal plane of symmetry; the molecule is achiral.

Number of stereoisomers = a molecule with n stereogenic centers (and for which a meso isomer isn’t possible) will have 2n stereoisomers.

Resolution of Racemic Mixtures

  • There are two basic ways that one can separate the

  • enantiomers in a racemic mixture:

  • Biological Resolution : Using a microbe which metabolizes

    one specific enantiomer leaving the other alone.

  • Chemical Resolution:The racemate is converted to two

    diastereoisomers. Once separated the diasteriosomeric

    forms are converted back to enantiomers in separate


Z isomer

E isomer

  • A competely unambiguous system, based on a set of group priority rules, assigns a Z (German, zusammen for together) or

    E (German, entgegen for opposite) to designate the stereoisomers.

  • Z is equivalent to cis and E is equivalent to trans.

Today’s Quote

One learns one’s most valuable lessons through hardships.


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