CHE 8A Lecture 11: Ring Flips
Chem 008A Tuesday 11/6/18 Lecture II
Rings have ring Strain → bond angle Structure -torsional Strain
r
~
30kcal
Imo
I ~
28kcal
Imo
I 1-1 6.5 kcal /mot
H H
XH
#H
12 eclipsing c-HH
)fitit
-¥⇒← It
a
.
It It
Some
bond angle Strain
up back edge away
o
-X¥
E
lower edge atos
Chair cyclohexane
107-1100 bond angles → 100% Staggered
Hit 1h14 Staggered
HCha H
.
HChair cyclohexane n O kcal /mot
Utz µ HStrain
it T
gauche
How to draw a chair → 3 Sets of parallel lines
7
11A " Lines "B'' Lines
it C
''
Lines
Right pointing chair
left pointing chair
Each C of cyclohexane has 2 H attached → I up , I down
→
# PT Iaxial ,t equatorial
H
H
ft Iv p
Il
it it €Atf
[HT
Ii
H
can rotate bonds can → up I down Stay same
down (if -H
^have rotamers .face of mot . the
group is
axial It → point Straight vpl down µ)on Its const . ( stay cis )
parallel to central axis LStay trans )
down
equatorial It → point out around
equator away from axes
when we rotate -axt equatorial switch → Ring Flip
Hax
,
Steric
,
hind = trans annular Hax
IHStrain I
Hea
'Hea I•
*afoot
"
'it Is ¥4 ,
Hea
Hax T
boat conformer Hax
eclipsing C- It in
Center 4C
