Butane - Rotate With C3-C4 Bond.: C H C H C H CH H H H H
Butane - Rotate With C3-C4 Bond.: C H C H C H CH H H H H
Butane - Rotate With C3-C4 Bond.: C H C H C H CH H H H H
H3C C C CH3 H
H2 H2 H
H H
butane ---->>> rotate with C3-C4 bond.
H H
H H
H H H H H H
H HH H H
H
Fully eclipse Gauche Eclipse Anti
Has more Has No Torsional Has Less Has No Torsional
Torsional strain strain, but there is Torsional strain strain and there is no
a steric strain by streric strain by alkyl
two proximal methyl groups (which are far apart)
groups.
CH3
1 2 3 4 5 6
H3C C C C C CH3 H
H H2 H2 H2 H
H H
2-methylhexane ---->>> rotate with C3-C4 bond.
H H
H H
H H H H H H
H HH H H
H
Fully eclipse Gauche Eclipse Anti
Has more Has No Torsional Has Less Has No Torsional
Torsional strain strain, but there is Torsional strain strain and there is no
an electron repulsion electron repulsion
between two alkyl between two alkyl
groups (which are nearby) groups (which are far away)
H H
H
H H H H
H
Obtain the missing conformer after 180o rotation for A and B. Also, predict which is more stable
from each case. Also, show the name of each alkane.
H H
H
180o H
H H
rotation
H H
H H n-pentane
H H
180o (Clock-wise)
180o (Clock-wise)
H H H H
180o
H rotation H
H H H
H H
H
n-pentane
Skew
(B)
Br
Br
Eclipse
(II) Below, obtain the IUPAC name for the compound from both conformations (A & B).
A: B:
2'
R
2
R R
R
R
R R
2'
R
2
R R
3'
R
3 R
3'
3 R
R
R R
R
4
R
R
R
4
more stable
(it has less 1,3-diaxial interaction)
up
down
more stable
(it has less 1,3-diaxial interaction)
H H H
H
H H
H
H H
H
CIS
CIS
up
eq & ax down ax & eq
up
equally stable althoough there is a down
1,3-diaxial interaction via one axial-Me equally stable althoough there is a
1,3-diaxial interaction via one axial-Me
1,2-dimethyl
ax & ax
cyclohexane eq & eq
TRANS
TRANS
up down
eq & eq
ax & ax
down up
eq-eq combination is more stable, eq-eq combination is more stable,
because the conformation has no because the conformation has no
1,3-diaxial interaction 1,3-diaxial interaction
ax & ax eq & eq
CIS
CIS
down
up
eq & eq ax & ax
down
up
up eq & ax down
ax & eq
down up
equally stable althoough there is a equally stable althoough there is a
1,3-diaxial interaction via one axial-Me 1,3-diaxial interaction via one axial-Me
ax & eq eq & ax
CIS
CIS
up
eq & ax down
ax & eq
up
down
equally stable althoough there is a
1,4-dimethyl 1,3-diaxial interaction via one axial-Me equally stable althoough there is a
1,3-diaxial interaction via one axial-Me
cyclohexane
ax & ax
eq & eq
TRANS
TRANS
up down
eq & eq ax & ax
down up
eq-eq combination is more stable, eq-eq combination is more stable,
because the conformation has no because the conformation has no
1,3-diaxial interaction 1,3-diaxial interaction