Alkenes

University of Babylon / College of Pharmacy
Department of Pharmaceutical Chemistry

Reference text:
1-Robert T. Morrison
2-McCurry

Lecture No. 1,2 22/2/2018

Introduction:

Structure and Properties
Organic chemistry is the chemistry of the compounds of carbon.
The misleading name "organic" is a relic of the days when chemical compounds were divided into two classes, inorganic and organic, depending upon where they had come from. Inorganic compounds were those obtained from minerals; organic compounds were those obtained from vegetable or animal sources, that is from material produced by living organisms.

The structural theory
The structural theory is the basis upon which millions of facts about hundreds of thousands of individual compounds have been brought together and arranged in a systematic way . The structural theory is the framework of ideas about how atoms are put together to make molecules .It has to do with the order in which atoms are attached to each other, and with the electrons that hold them together . It has to do with the shapes and sizes of the molecules that these atoms form, and with the way that electrons are distributed over them.

The chemical bond before 1926
In 1916 two kinds of chemical bond were described : the ionic bond by Walther Kossel (in Germany ) and the covalent bond G.N. Lewis (of the university of California ) .Both Kossel & Lewis based their ideas on the following :
A positively charged nucleus is surrounding by electronic arranged in concentric shells or energy levels . There is maximum number of electrons that can be accommodated in each shell : two in the first shell, eight in the second shell, eight or eighteen in the third shell, and so on . The greatest stability is reached when the outer shell is full, as in the noble gases .
Both ionic and covalent bonds arise from the tendency of atoms to attain this stable configuration of electrons .
The ionic bond results from transfer of electrons, as, for example, in the formation of lithium fluoride .
The covalent bond results from sharing of electrons, as, for example, in the formation of hydrogen molecule .


Quantum mechanics
In 1926 there emerged the theory known as quantum mechanics, developed, in the form most useful to chemists, by Erwin Schrodinger (of the university of Zurich) . He worked out mathematical expressions to the motion of an electron in terms of its energy. These mathematical expressions are called wave equations, since they are based upon the concept that electrons show properties not only particles but also of waves .

Atomic Orbitals
A wave equation can not tell us exactly where an electron is at any particular moment, or how fast it is moving ; it does not permit us to plot a precise orbit about the nucleus . Instead, it tell us the probability of finding the electron at any particular place . The region in space where an electron is likely to be found is called an orbital .

Electronic configuration ; Pauli exclusion principle
There are a number of " rules " that determine the way in which the electrons of an atom may be distributed, that is, that determine the electronic configuration of an atom . The most fundamental of these rules is the Pauli exclusion principle : only two electrons can occupy any atomic orbital, and to do so these two must have opposite spine . These electrons of opposite spine are said to be paired . Electrons of like spine tend to get as far from each other as possible .These tendency is the most important of all the factors that determine the shapes and properties of molecules .

Molecular orbitals
In molecules, as in isolated atoms, electrons occupy orbitals, and in accordance with much the same "rules" . These molecular orbitals are considered to be centered about many nuclei, perhaps covering the entire molecules ; the distribution of nuclei and electrons is simply the one that results in the most stable molecule .
To make the enormously complicated mathematics more workable, two simplifying assumptions are commonly made : (a) that each pair of electrons is essentially localized near just two nuclei, and (b) that the shapes of these localized molecular orbitals and their disposition of atomic orbitals in the component atoms .
The idea of localized molecular orbitals?or what are might call bond orbitals? is evidently not a bad one, since mathematically this method of approximation is successful with most (although not all ) molecules .


The covalent bond
Now let us consider the formation of a molecule. For convenience we shall picture this as happening by the coming together of the individual atoms, although most molecules are not actually made this way. We make physical models of molecules out of wooden or plastic balls that represent the various atoms; the location of holes or snap fasteners tells us how to put them together.

Hybrid orbitals: sp
Let us next consider beryllium chloride, BeCl2 .Beryllium has no unpaired electrons. How are we to account for its combining with two chlorine atoms? Bond formation is an energy-releasing (stabilizing) process, and the tendency is to form bonds and as many as possible even if this results in bond orbitals that bear little resemblance to the atomic orbitals we have talked about. If our method of mental molecule-building is to be applied here, it must be modified. We must invent an imaginary kind of beryllium atom, one that is about to become bonded to two chlorine atoms.

Hybrid orbitals: sp²
Next , let us look at boron trifluoride, BF? .Boron has only one unpaired electron, which occupied a 2p orbital .

University of Babylon / College of Pharmacy
Department of Pharmaceutical Chemistry

Reference text:
1-Robert T. Morrison
2-McCurry

Lecture No. 1,2 22/2/2018

Introduction:

Structure and Properties
Organic chemistry is the chemistry of the compounds of carbon.
The misleading name "organic" is a relic of the days when chemical compounds were divided into two classes, inorganic and organic, depending upon where they had come from. Inorganic compounds were those obtained from minerals; organic compounds were those obtained from vegetable or animal sources, that is from material produced by living organisms.

The structural theory
The structural theory is the basis upon which millions of facts about hundreds of thousands of individual compounds have been brought together and arranged in a systematic way . The structural theory is the framework of ideas about how atoms are put together to make molecules .It has to do with the order in which atoms are attached to each other, and with the electrons that hold them together . It has to do with the shapes and sizes of the molecules that these atoms form, and with the way that electrons are distributed over them.

The chemical bond before 1926
In 1916 two kinds of chemical bond were described : the ionic bond by Walther Kossel (in Germany ) and the covalent bond G.N. Lewis (of the university of California ) .Both Kossel & Lewis based their ideas on the following :
A positively charged nucleus is surrounding by electronic arranged in concentric shells or energy levels . There is maximum number of electrons that can be accommodated in each shell : two in the first shell, eight in the second shell, eight or eighteen in the third shell, and so on . The greatest stability is reached when the outer shell is full, as in the noble gases .
Both ionic and covalent bonds arise from the tendency of atoms to attain this stable configuration of electrons .
The ionic bond results from transfer of electrons, as, for example, in the formation of lithium fluoride .
The covalent bond results from sharing of electrons, as, for example, in the formation of hydrogen molecule .


Quantum mechanics
In 1926 there emerged the theory known as quantum mechanics, developed, in the form most useful to chemists, by Erwin Schrodinger (of the university of Zurich) . He worked out mathematical expressions to the motion of an electron in terms of its energy. These mathematical expressions are called wave equations, since they are based upon the concept that electrons show properties not only particles but also of waves .

Atomic Orbitals
A wave equation can not tell us exactly where an electron is at any particular moment, or how fast it is moving ; it does not permit us to plot a precise orbit about the nucleus . Instead, it tell us the probability of finding the electron at any particular place . The region in space where an electron is likely to be found is called an orbital .

Electronic configuration ; Pauli exclusion principle
There are a number of " rules " that determine the way in which the electrons of an atom may be distributed, that is, that determine the electronic configuration of an atom . The most fundamental of these rules is the Pauli exclusion principle : only two electrons can occupy any atomic orbital, and to do so these two must have opposite spine . These electrons of opposite spine are said to be paired . Electrons of like spine tend to get as far from each other as possible .These tendency is the most important of all the factors that determine the shapes and properties of molecules .

Molecular orbitals
In molecules, as in isolated atoms, electrons occupy orbitals, and in accordance with much the same "rules" . These molecular orbitals are considered to be centered about many nuclei, perhaps covering the entire molecules ; the distribution of nuclei and electrons is simply the one that results in the most stable molecule .
To make the enormously complicated mathematics more workable, two simplifying assumptions are commonly made : (a) that each pair of electrons is essentially localized near just two nuclei, and (b) that the shapes of these localized molecular orbitals and their disposition of atomic orbitals in the component atoms .
The idea of localized molecular orbitals?or what are might call bond orbitals? is evidently not a bad one, since mathematically this method of approximation is successful with most (although not all ) molecules .


The covalent bond
Now let us consider the formation of a molecule. For convenience we shall picture this as happening by the coming together of the individual atoms, although most molecules are not actually made this way. We make physical models of molecules out of wooden or plastic balls that represent the various atoms; the location of holes or snap fasteners tells us how to put them together.

Hybrid orbitals: sp
Let us next consider beryllium chloride, BeCl2 .Beryllium has no unpaired electrons. How are we to account for its combining with two chlorine atoms? Bond formation is an energy-releasing (stabilizing) process, and the tendency is to form bonds and as many as possible even if this results in bond orbitals that bear little resemblance to the atomic orbitals we have talked about. If our method of mental molecule-building is to be applied here, it must be modified. We must invent an imaginary kind of beryllium atom, one that is about to become bonded to two chlorine atoms.

Hybrid orbitals: sp²
Next , let us look at boron trifluoride, BF? .Boron has only one unpaired electron, which occupied a 2p orbital .