bremsstrahlung German for “breaking radiation.”
Electromagnetic radiation is emitted when a charged
particle changes its velocity or as it changes direction
due to near collisions with other particles.
bridged carbocation A CARBOCATION(real or hypo-
thetical) in which there are two (or more) carbon atoms
that could, in alternative LEWIS FORMULAe, be desig-
nated as CARBENIUM CENTERs but which are instead
represented by a structure in which a GROUP(a hydro-
gen atom or a hydrocarbon residue, possibly with sub-
stituents in noninvolved positions) bridges these
potential carbenium centers. One can distinguish “elec-
tron-sufficient bridged carbocations” from “electron-
deficient bridged carbocations.” Examples of the
former are phenyl-bridged ions (for which the trivial
name “phenonium ion” has been used), such as
depicted in Figure (A). These ions are straightforwardly
classified as CARBENIUM IONs. The latter type of ion
necessarily involves three-center bonding.
The hydrogen-bridged carbocation (B) contains a
two-coordinate hydrogen atom. Hypercoordination—
which includes two-coordination for hydrogen and at
least five-coordination for carbon—is generally
observed in bridged carbocations. Structures (C) and
(D) contain five-coordinate carbon atoms.
See alsoMULTICENTER BOND; NEIGHBORING-GROUP
PARTICIPATION.bridging ligand A bridging ligand binds to two or
more CENTRAL ATOMs, usually metals, thereby linking
them together to produce polynuclear COORDINATION
entities. Bridging is indicated by the Greek letter μ
appearing before the ligand name and separated by a
hyphen.
See alsoFEMO COFACTOR.Bronsted acid(Bronsted-Lowry acid) A molecular
entity capable of donating a HYDRONto a base (i.e., a
“hydron donor”) or the corresponding chemical
species. For example: H 2 O, H 3 O+, CH 3 CO 2 H, H 2 SO 4 ,
HSO 4 – , HCl, CH 3 OH, and NH 3.
See alsoCONJUGATE ACID–BASE PAIR.Bronsted base(Bronsted-Lowry base) A molecular
entity capable of accepting a HYDRONfrom an acid
(i.e., a “hydron acceptor”) or the corresponding chemi-
cal species. For example: OH–, H 2 O, CH 3 CO 2 – ,
HSO 4 – , SO 4 2–, and Cl–.
See alsoCONJUGATE ACID–BASE PAIR.Bronsted relation The term applies to either of the
following equations:
kHA/p= G(KHAq/p)α
kA/q= G(KHAq/p)–β
(or their logarithmic forms) where α, β, and Gare con-
stants for a given reaction series (αand βare called
“Bronsted exponents”), and kHAand kAare catalytic
coefficients (or rate coefficients) of reactions whose
rates depend on the concentrations of HA and/or of A–.
KHAis the acid dissociation constant of the acid HA; p
is the number of equivalent acidic protons in the acid
HA; and qis the number of equivalent basic sites in its
conjugate base A–. The chosen values of pand qshould
always be specified. (The charge designations of HA
and A–are only illustrative.) The Bronsted relation is
often termed the Bronsted CATALYSIS LAW. Although34 bremsstrahlung