Organic Chemistry Chapter 5 – Stereochemistry, Chirality, and Optical Activity | Lecture and Exam 2 Summary

09/19 chs ,
SecS 1 5 2 55 5 Start of
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Exam 2
5 1 Steriosomers
.




Compounds that differ from other in the 3-D spatial of their atoms , but not the connectivity
each
only arrangement
-



,



of the atoms
Two kinds :




-
Constitutional isomers Same molecular formula but different :
, connectivity of atoms (different structure format
-

Stereoisomers Same Molecular formula
: d connectivity but different spatial arrangent of
,
atoms (cisor trans !)
↳ Cis alkene has two hydrogen atoms on same side as double bond

↳ trans has two hydrogens on opposite sides of double bond

-

in such cases ,
the double bond is not strisomerica cannot be described as cis or trans

5 2 Chirality
. a Chiral molecules
-



tetrahedral Carbon w/ 4 groups ,
- Chiral center


Can be arranged
↳
in two ways
H OH H
.,,
Of
Et
Vechiral center- rotate or flip the first drawing W/
or it
> -no matter how much you - cannot get it to match
-x may
has two steriosomers
↳ non superimposable
= Second
drawing
Bra
At
-
⑭ *Chiral Center




the ringhas different paths no matter which
way you go ,
3rd one *

Br H
a

5) no chival center - identical paths

Chiral + Achival Objects

Chiral If it lacks reflectional
Symmetry (internal plane of symmetry) example
: :




h
OH
#
-

trans
Sec-butyl alcohol . 1 .


2-dimethylcyclohexane
If molecule has plane of it cannot be chival
a a
symmetry
↳ called Achival example :




·
-




1


Just because it doesn't have a plane of doesn't its chiral
symmetry assume

↳ Inversion :
reflection about a point (rather than a plane) , example :




*

, . 2 Enantiomers
5
·
When a compound is chiral ,
will have a non superimposable mirror image called
,
entationer example : ,




↳ left hands


I
rights

O a chival compound will have one enautioner -
not mors a




. S Optical
5 activity
enantiomers exhibit Physical properties for , example, Compare mpdBp for these



*
[0 =7
Mp : 25 :
°

mp : 25 c




Bp : 231'c BD : 231° C


Enantiomers exhibit different behavior When exposed to a plane-polarized light




i diwon
·




of motion of the light beam
↑
magnetic Wave



Plane polarized light notice each field is located in a planet they are perpendicular to each other


↓ 1: Shown / as polarization of the
light wave

↳ allowed to pass
When light passes through polarized Filter, photons of particular Polarization through
a
only a are


↳ polarized light
giving a rise to


Polarimetry
Optically active: Certain compounds rotate the plans of polarized light
organic
Compounds lacking
↳
this
ability said to Optically inactive
↳ Carb
were be


, measured WI a polarimeter

enantiomers will rotate the plane -
polarized light in equal amounts but in opposite directions

Specific rotation

Observed rotation dependent : on # of molecules that the
light encounters as it travels through the solution


Optical activity is measured using a
very dilute solution

Specific Rotation

Specific rotation : ( =brotationmetese(dm 10cm) = + rotation =
dextrorotatory
↑
but
equal in magnitude concentration (g(mi) rotation Levorotatory
-
=

direction
[a]] Br opposite
-
in
Br

⑪ E
- N D = line of sodium


[a]3 =
-


23 ! .
[a] = +
23 ) .




1)-2-Bromobutane (t)- 2-Bromobutane


[1) -
2 Bromobutane
-

(d) 2 - Bromobutane
-