150
5.111 Lecture Summary #9 Friday, September 26, 2014
Readings for today: Sections 2.1-2.3 – Ionic Bonds, Sections 2.14-2.16 - The Strengths and
Lengths of Covalent Bonds
Read for Lecture #10: Section 2.5 – 2.8 Lewis Structures (Same sections in 5 and 4 ed.) th th
___________________________________________________________________________
Topics: I. Trends in Periodic Table Continued
A. IE (completed in lecture #8)
B. Electron affinity (completed in lecture #8)
C. Electronegativity
D. Atomic and ionic radii and Isoelectronic atoms
II. Ionic bonds
III. Covalent bonds
IV. Polar Covalent bonds
_________________________________________________________________________________________________________________
C. ELECTRONEGATIVITY (c)
Electronegativity is the net
ability of an atom to attract
an electron from another
atom. Linus Pauling first
proposed this idea in 1932.
Mulliken's electronegativity scale developed two years later is conceptually easier.
electronegativity (c) µ ( + )
An atom with high electronegativity is an electron .
An atom with low electronegativity is an electron .
, In their own words:
Bacteria have developed resistance to many
antibiotics, and there is need for current and future
scientists to develop new types of antibiotics.
Kateryna discusses her research on enzymes that
catalyze a carbon-chlorine bond-formation, and how
taking advantage of chlorine’s electronegativity may
lead to new medications to fight bacteria and other
“bugs” that make us sick.
Image from "Behind the Scenes at MIT”. The Drennan Education Laboratory.
Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License.
Electronegativity in Drug Design: Fluorine Atoms in Drugs
Although carbon-fluorine (C-F) bonds are not known to be present in the human body,
C-F bonds are incorporated into a number of drugs.
H2C CH2 H2 CF3
H
C N H2
CH H2C NH H2C CH2 C
C
F H 2C N
H H
N C N CH2 C O CH CH2 N
O H H2 H2
HC C C C C C C C
H2 C C C N C
H2 H N
H2C HC C C C
C C
HO C C C C CH H2
O C HC CH
C C C F H
H C CH NH2 O
HC CH F C
O
Cipro®
O
Paxil® C Januvia®
broad-spectrum antibiotic anti-depressant F
F
anti-diabetic
Why??? One reason is that F, due to its high electronegativity, can make a molecule
electron ____________ if the fluorine is appropriately positioned on an aromatic ring.
Since oxidation involves losing an electron,
a drug that is electron-poor will be
to oxidize.
liver Drugs are metabolized by a class of proteins
in the liver called cytochrome P450 (or
Cyp) enzymes.
Fluorination can increase a drug’s
metabolic stability by making it less
susceptible to oxidation by Cyp enzymes.
Cyp enzyme bound to a drug
For a brief article on a strategy developed in the Buchwald lab at MIT for installing fluorine into medically
relevant molecules, see http://web.mit.edu/newsoffice/2009/drug-synthesis-0813.html.
D. ATOMIC and IONIC RADII
The atomic size is defined as the value of r below which 90%
of electron density is contained.
2
5.111 Lecture Summary #9 Friday, September 26, 2014
Readings for today: Sections 2.1-2.3 – Ionic Bonds, Sections 2.14-2.16 - The Strengths and
Lengths of Covalent Bonds
Read for Lecture #10: Section 2.5 – 2.8 Lewis Structures (Same sections in 5 and 4 ed.) th th
___________________________________________________________________________
Topics: I. Trends in Periodic Table Continued
A. IE (completed in lecture #8)
B. Electron affinity (completed in lecture #8)
C. Electronegativity
D. Atomic and ionic radii and Isoelectronic atoms
II. Ionic bonds
III. Covalent bonds
IV. Polar Covalent bonds
_________________________________________________________________________________________________________________
C. ELECTRONEGATIVITY (c)
Electronegativity is the net
ability of an atom to attract
an electron from another
atom. Linus Pauling first
proposed this idea in 1932.
Mulliken's electronegativity scale developed two years later is conceptually easier.
electronegativity (c) µ ( + )
An atom with high electronegativity is an electron .
An atom with low electronegativity is an electron .
, In their own words:
Bacteria have developed resistance to many
antibiotics, and there is need for current and future
scientists to develop new types of antibiotics.
Kateryna discusses her research on enzymes that
catalyze a carbon-chlorine bond-formation, and how
taking advantage of chlorine’s electronegativity may
lead to new medications to fight bacteria and other
“bugs” that make us sick.
Image from "Behind the Scenes at MIT”. The Drennan Education Laboratory.
Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License.
Electronegativity in Drug Design: Fluorine Atoms in Drugs
Although carbon-fluorine (C-F) bonds are not known to be present in the human body,
C-F bonds are incorporated into a number of drugs.
H2C CH2 H2 CF3
H
C N H2
CH H2C NH H2C CH2 C
C
F H 2C N
H H
N C N CH2 C O CH CH2 N
O H H2 H2
HC C C C C C C C
H2 C C C N C
H2 H N
H2C HC C C C
C C
HO C C C C CH H2
O C HC CH
C C C F H
H C CH NH2 O
HC CH F C
O
Cipro®
O
Paxil® C Januvia®
broad-spectrum antibiotic anti-depressant F
F
anti-diabetic
Why??? One reason is that F, due to its high electronegativity, can make a molecule
electron ____________ if the fluorine is appropriately positioned on an aromatic ring.
Since oxidation involves losing an electron,
a drug that is electron-poor will be
to oxidize.
liver Drugs are metabolized by a class of proteins
in the liver called cytochrome P450 (or
Cyp) enzymes.
Fluorination can increase a drug’s
metabolic stability by making it less
susceptible to oxidation by Cyp enzymes.
Cyp enzyme bound to a drug
For a brief article on a strategy developed in the Buchwald lab at MIT for installing fluorine into medically
relevant molecules, see http://web.mit.edu/newsoffice/2009/drug-synthesis-0813.html.
D. ATOMIC and IONIC RADII
The atomic size is defined as the value of r below which 90%
of electron density is contained.
2
