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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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Presentation Transcript
slide1

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
slide2

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.

slide4

Carboxylic Acid

Carboxylate ion

slide5

Electron-withdrawing groups stabilize a conjugate base,

making a carboxylic acid more acidic.

slide6

Electron-donating groups destabilize a conjugate base,

making a carboxylic acid less acidic.

amines

NH3 + H2O NH4+ + OH-

Amines

RNH2, ArNH2 Primary, 1o Amines

R2NH, Ar2NH Secondary, 2oAmines

R3N, Ar3N Tertiary, 3o Amines

N,N-dimethylethylamine

butylamine

N-methylpropylamine

slide19

สารประกอบเอมีนที่มีฤทธิ์เป็นยาสารประกอบเอมีนที่มีฤทธิ์เป็นยา

slide23

Quote of The Day

Think like a wise man

but express yourself like

an ordinary one.

จงคิดเหมือนปราชญ์

แต่แสดงออกเหมือนสามัญชน

slide24

Stereochemistry

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

Stereoisomers

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.

slide25

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).
slide26

Mirror

180° rotation

slide29

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].
slide30

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.

(http://www.cem.msu.edu/~reusch/VirtualText/sterism2.htm#isom12)

slide31

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

slide32

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

slide33

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.

slide34

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
slide35

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

an atom attached to 4 different atoms or groups.

(chiral carbon)

slide36

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.
slide37

The assignment of the prefixes depends on the

application of two rules:

The Sequence Rule

The Viewing Rule

Right-Handed

Left-Handed

slide38

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–.
slide39

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–

slide40

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.
slide41

Assign Priorities

Twist the lowest

priority to the

back

Rotate Priorities

slide42

Priorities

2-Bromobutane

View &

Assign

(S)-2-Bromobutane

slide44

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.

slide45

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).

slide47

Compounds Having Two or More Stereogenic Centers

Stereocenter 2

Stereocenter 1

adrenaline

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

slide48

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

slide49

Diastereomers

  • 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.

slide50

Diastereomers

Diastereomers

slide51

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.

slide52

Relationships Between Stereoisomers

Stereoisomers

Enantiomeric with

Diastereomeric with

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

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

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

Pseudoephedrine

and

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

Pseudoephedrine

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

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

slide54

Meso Isomer:

an achiral molecule with 2 or more chiral centers and

an internal plane of symmetry; the molecule is achiral.

slide55

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

slide56

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

containers.

slide57

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.
slide59

Today’s Quote

One learns one’s most valuable lessons through hardships.

ชีวิตจะได้รับบทเรียนที่มีค่ามากที่สุดท่ามกลางความทุกข์ยาก

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