TWO REACTION PATHS

1
Reactions of dibromo-benzenes and dibromo-xylenes
at Si(111) followed one
molecule at a time
Sergey Dobrin, Rajamma K. Harikumar,
Chérif F. Matta,

Ioannis D. Petsalakis, John C. Polanyi and
Giannoula Theodorakopoulos
Department of
Chemistry, University of Toronto, Toronto,
Ontario, Canada M5S 3H6
PARENT 1,2 Nearest-neighbour
PARENT 1,2 Br PAIR-SEPARATION (Å)
7.7
Benzene-mediated mechanism
Br-Pairs with benzene residue attached to the
surface 70
3 Å
N (r)
6.7
9.0
4.6
10.2
11.5
13.9
Arrows indicate the target dangling bonds (Si
adatoms and Si rest atoms) accessible by
stretching of the C-Br bonds along the direction
of the C-Br bonds, 45.
r (Br.. Br) (Å)
PARENT 1,4 Br PAIR-SEPARATION (Å)
PARENT 1,4 Nearest-neighbor
7.7
Benzene-mediated mechanism
Br
Br
Br
6.5 Å
N (r)
3 Å
7.7
11.5
6.7
15.4
10.2
13.9
4.6
9.0
6.7
10.2
13.9
16.8
9.0
r (Br.. Br) (Å)
1,2-XDB on Si(111)-7x7
1,2 XDB Br PAIR-SEPARATION (Å)
1,2 XDB Reactive pathway (Å)
I
I
N 120
II
II
7.7
Si rest atom Br atom
Distance between each Br atom in the 4.5 to 5.5 Å
N (r)
6.7
11.5
10.2
9.0
13.9
4.6
15.4
r (Br..Br) Å
1,2 XDB Nonreactive pathway (Å)
1,4 XDB Br PAIR-SEPARATION (Å)
H
H
N 111
Br
Br
11.5 Å
C
C
H
H
7.5 Å
N (r)
7.7
13.3
10.2
13.9
6.7
XDB is 15 times less reactive
than DBB!!!
r (Br..Br) Å
HALOGEN - MEDIATED
TWO REACTION PATHS
BENZENE - MEDIATED
BENZENE mediated path is more important for
1,2- than for 1,4- conformers
PARENT GEOMETRY GOVERNS DAUGHTER GEOMETRY