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Explain formation of molecular orbitals
In atoms electrons occupy atomic orbitals, electrons in molecules occupy molecular orbitals. Molecular orbitals are generated by combining atomic orbitals. The number of orbitals formed is equal to the number of atomic orbitals that combine. Each molecular orbital can hold two electrons.
What are bonding molecular orbitals/antibonding molecular orbitals
One of the molecular orbitals is law and energy than either of the Tomich orbitals that combined to produce it, this is called a bonding molecular orbitals. The other molecular orbital is known as an anti bonding molecular orbital and is of higher energy than either of the atomic orbitals that combined to produce it.
Difference between the bonding molecular orbital is polar/non-polar molecules
In a nonpolar molecule, the molecular orbital will be symmetrical around the two atoms. In a polar molecule, the molecular orbital will be asymmetric around the two atoms.
Sigma bonds and their formation
Molecular orbital is formed by an Overlap of atomic orbitals along the axis of the bonds. I.e. a covalent bond, called a sigma bond. This is usually referred to as an end on overlap.
Pi bonds
To parallel P atomic orbitals that are perpendicular to the axis of the bond can overlap laterally or side on to form a pi bond. The overlap of atomic orbitals is much less effective than the end of overlap. Pie bonds are weaker than Sigma bonds.
What is hybridisation of orbitals
Hybridisation is the process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals. Which are degenerate
Hybridisation of alkanes
In alkanes the four sp3 orbitals on each carbon atom will overlap and end on with four other orbitals, i.e. then the hydrogen ___ orbitals and one sp3 orbital on the other carbon atom. Four sigma bonds will be formed and they will adapt a tetrahedral arrangement.
Hybridisation of alkenes
In alkenes, the 3 sp2 orbitals adapt a trigonal planar arrangement. In Ethene each carbon atom uses its three sp2 orbitals two form Sigma bonds with two hydrogen atoms and with other carbon. The unhybridized 2p orbital left on the carbon atoms overlaps the side to form a pi bond.
Hybridisation of alkynes
In alkynes the 2 sp2 orbitals in each carbon form sigma bonds with the other carbon atom. The unhybridized 2p orbitals overlap side on to form pi bonds
Hybridisation of benzene
In benzene, c6h6, each carbon atom is sp2 hybridised and the 3 half-filled sp2 orbitals form sigma bonds with a hydrogen aion and the two neighbouring carbon atoms. This leaves an electron occupying a p-orbital on each carbon atom. Each of there p-orbitals overlap side on with p orbitals on neighbouring carbon atoms, a pi electron bond is formed
What is a chromophore
A chromophore is a group of atoms within a molecule which is replicable for absorption of light. Chromophores Exist in molecules, with conjugated system brackets attract double bonds. Delocalised electrons between atoms are conjugate system has alternating sigma and pi bonds
Why some organic molecules appear coloured
Absorption of electromagnetic energy can cause electrons to be parallel from the highest occupied molecular orbital ‘homo’ to the coho. If the wavelength of light absorbed lies in the ems then the color observed will be complementary to that absorbed
Why most organic molecules are colourless
Most organic molecules are colourless as the gap between the homo and lumo is large, this means that light from uv region is absorbed and so molecule appears colourless
What happens to the frequency of light absorbed when the conjugated system contains more atoms?
If there are more atoms in the conjugated system then there is a smaller energy gap between homo/lumo. Therefore lower frequency and lower energy is absorbed.
what is an isomer
An isomer is a molecule with the same molecular formula but different structural formula
What is a stereoisomers
A stereoisomer is when the order of bonding in each atom is the same but the spatial arrangement of the atom is different in each bond
What are geometric isomers
A geometric isomer occurs when the arrangement of the atom is different in each isomer
Under what circumstances do geometric isomers occur
Occur when there is rotation around a carbon to carbon double bond, also there must be two different groups attached to each of the carbon atoms that make up the bond
What is meant by cis and trans
Cis is groups on the sdame side of the double bond, trans is groups on opposite side of the double bond
How do properties of geometric isomers differ
Geometric isomers can have different physical properties
What are optical isomers
They contain the same number and kinds of atoms and bonds, they are non-super imposable mirror images
When do optical isomers occur
When four different groups are arranged tetrically around a central carbon atom (chiral carbon)
How do properties of optical isomers occur
Identical but on light
Effect of enantiomers on polarise light
One enantiomer will rotate light in one direction and the other enantiomer in the opposite direction by the same difference. as there is an equal amount of each enantiomer, the rotation would cancel
What is a racemic mixture and why are they described as being optically inactive
A racemic mixture is an equal mixture of enantiomers, of a chiral molecule
What is infrared spectroscopy used for
Its used to identify specific functional groups in organic molecules
Explain how infrared spectroscopy works
Infrared spectroscopy intakes infrared at organic molecules which causes their bonds to vibrate in different ways. The wavelengths which are absorbed depend on the type of chemical bondand the atoms at the end of these bonds
What is the general rule regarding the weight of atoms and bond strength
Lighter atoms are converted by stronger bonds (higher energy radiation absorbed), heavier atoms are connected by weaker bonds (lower energy radiation absorbed)
What is nass spectroscopy used for
Mass spectroscopy is used to determine the accurate molecular mass and structural features of a compound
How does mass spectroscopy work
A small sample of an organic compound is bombarded by high energy electrons. This removes electrons from the organic molecule generating positively charged molecular ions known as parent ions. These molecular ions then break into smaller positively charged ion fragments
Explain how proton nmr spectroscopy works
Nuclei of atoms behave like tiny magnets and in a strong magnetic field some align with the field (lower energy) whilst the rest align against it (higher energy). The absorption of radiation in the radio frequency of the electromagnetic spectrum causes the 1h nuclei to flip from the lower to higher energy alignment. As they fall back from higher to lower energy alignment emitted radiation is detected and plotted on a spectrum
How are proton environments identified
The fragments
What is homlytic fission
The neutral species are formed and each species has an unpaired electron so is a free radical. I single headed curly arrow is used. Not useful in synthetic chemistry as complex mixture of products form due to the chain reaction
what is heterolytic fission
Normally occurs when polar covalent bonds are broken, the more electronegative atom retains both electrons. A double headed curly are all as used as pair of electrons are moving.
Talk about nucleophiles
A nucleophile is attracted to positively charged species i.e. a nucleus. Nucleophiles or negatively charged or neutral molecules that are electron rich or have lunch pairs of electrons. A carbon to carbon double bond is electron rich. Nucleophiles provide electrons for making of a new bond.
Talk about electrophiles
The electro file is attracted to negatively chargedSpecies, electrophiles are negatively charged or neutral molecules that are electron deficient, they may have a polarised pie bond, or may have an atom that is positive. Electrophiles accept electrons in chemical reactions
What are haloalkanes
Haloalkanes are halogen substituted Alkenes, named using bromo, chloro etc.(naming in book)
What are different classifications for haloalkanes
In book
what is nucleophilic substitution reaction
A nucleophillic substitution is when a nucleophile substitutes itself for the halogen atom, this can occur because the positive charge on carbon atom due to polar bonds makes it act like an electrophile
What are the different mechanisms for a nucleophilic substitution reaction
There are two mechanisms for nucleophilic substitution reactions. SN1 and SN2
Talk about SN1 mechanism
The SN1 mechanism is a two step process. Step 1 is the slow rate determining step, the haloalkane undergoes heterolytic fission to form a carbocation intermediate. Step 2 is the fast step and it involves nucleophillic attack on the carbocation by a nucleophile.
Talk about SN2 mechanism
The SN2 mechanism involves only one continuous step. The nucleophile attacks the carbon atom from the side opposite the carbon to halogen bond and begins to form a covalent bond with it. At the same time the carbon to halogen Bond begins to break. A transition state is reached, this adapts a trigonal know bipyramidal structure. The reaction is complete by the formation of our fill new bond and the complete break up of the carbon to halogen bond
How can the mechanism for Nucleophillic substitution be determined
In SN1 mechanism, a carbocation Intermediate is formed and this could be a primary, secondary or tertiary Carbocation. Alkyl groups have a positive effect. This means they are electron donating And can push electrons onto the positively charged carbon atom. Therefore it follows that tertiary carbocations you are the most stable. This supports that tertiary haloalkanes are most likely to react with a nucleophile In an SN1 mechanism.
What are factors affecting SN1 mechanism
The size of the alkyl groups in the haloalkane Is important, this is known as the something affect. In an SN2 mechanism THE NUCLEOPHILE Attacks the carbon atom from the opposite side of the halogen atom. In tertiary halo alkanes, attack from the side is likely to be hindered because the alkyl groups Will limit access to the carbon atom. Primary halo alkanes I have no more than one alkyl. Group attached to the halogen carbon atom and sort access to the carbon atom will be much easier therefore primary halo alkanes react with nucleophiles in SN2 mechanisms
What are factors affecting SN2 mechanism
The stability of the Carbocation is very important
What are the different types of reactions that involve halalkanes
The size of the alkyl group is very important (steric effect)
Talk about elimination reactions of haloalkanes
Halo alkanes can undergo elimination Reactions when they are heated under reflux with potassium hydroxide or sodium hydroxide. In the formation of the carbon to carbon double bond the carbon atom, together with a hydrogen atom on an adjacent carbon atom, has been removed or eliminated from the halo alkanes and not replaced, this reaction is known as base induced elimination
Explain how a sigma bond is formed
End on overlap of (two atomic) orbitals
A pi bond is formed as a result of sp2 hybridisation.
.
Explain what is meant by sp2 hybridisation
Mixing an s (atomic) orbital with two p (atomic) orbitals
State the type of hybridisation which is adopted by the carbon atoms in the aromatic ring.
sp2
Describe how pi bonds form
Orbitals overlap sideways
Explain fully why a solution of the salt sodium 4-hydroxybenzoate
has a pH greater than 7.
The (4-hydroxybenzoate) ion from the salt removes/ reacts with H+ from the water
OR
Conjugate base of a weak acid, removes/reacts with H+ from the water (1)
This results in the water equilibrium shifting to the right hand side
Geometric isomers:
can occur when there is restricted rotation around a carbon-carbon double bond or a carbon-carbon single bond in a cyclic compound
must have two different groups attached to each of the carbon atoms that make up the bond with restricted rotation
can be labelled cis or trans according to whether the substituent groups are on the same side (cis) or on different sides (trans) of the bond with restricted rotation
State what is meant by the term optical isomers
Non-superimposable mirror images of each other
Explain fully how this conjugated system gives rise to the red colour of carmine.
Electrons promoted/move from HOMO to LUMO/ The complementary colour(s) (to red) is absorbed
Explain why methanol is a suitable solvent for this extraction.
Similar polarities
Optically active
Must have a chiral centre (4 different atoms attached)
State the structural feature present that is responsible for the colour of these dye molecules.
alternating double and single bonds.
Explain fully how colour arises in these dye molecules.
Electrons move from HOMO to LUMO. (1)
Absorption of light (from the visible part of the spectrum) means that light of the complementary colour is seen.
Explain fully why this dye molecule will absorb a shorter wavelength of light than the other two dye molecules.
There is less conjugation
Larger gap/greater energy absorbed
what are amines
Amines are nitrogen containing organic compounds derived from ammonia, were one or more of the hydrogen atoms has been replaced by another a alkyl group. Bond angle 107 degrees
Physical properties of amines
Amines can form is in bonds between molecules, apart from in tertiary amines
Different classifications of amines
In book
Rules for naming amines
To name an amine prefix the word ‘amine’ with the names of the alkyl groups, if more than one alkyl group then name in alphabetical order.
Examples in book
what are ethers
Ethers are a homologous series, they have the general structure R-O-R’ where R and R’ are alkyl groups that can either be the same or different
Physical properties of ethers
Ethers cannot form hydrogen bonds between molecules, however they can form hydrogen bonds with water molecules
Rules for naming ethers
The longest carbon chain gives the parent name ending the part of the molecule with the oxygen atom is called -oxy
Look in book for examples
How can ethers be prepared
Ethers can be prepared by refluxing a haloalkane with an alkoxide in a nucleophillic substitution reaction
what are alkoxides
An alkoxide is the conjugate base of alcohol and therefore consist of an organic compound bonded to a negatively charged oxygen atom, written as RO-, they are named methoxy, ethoxy etc
What reactions can alkoxides be involved in
An alkoxide can react with a haloalkane under reflux to form an ether.
what are nitriles
A nitrile is any organic compound that has a c triple bond N functional group, the cyanide ion CN is a nucleophile.
Rules for naming nitriles
To name a nitrile, name the longest carbon chain and then add ‘nitrile’ to the end of the name
different methods to prepare alcohols
Read this In book now
Different reactions that alcohols can be induced in
Read this in book now
different methods to prepare Alkenes
There is a variety of methods to prepare Alkenes: dehydration of alcohols, base induced elimination of hydrogen halides from monohaloalkanes, the mechanisms of each of these is detailed in notes
Different reactions of Alkenes
Alkenes undergo addition reactions: with hydrogen to form alkanes (hydrogenation) and is catalysed with nickel/platinum: halogen to form (halogenation) a hydrogen halide to form monohaloalkanes (hydrohalogenation): water to form alcohols (hydration) and is catalysed by acids
What is makovnikovs rule (in book)
when H-X or H-OH is added to an unsymmetrical alkene, the major product is the one in which the H atom ends up attached to the c atom of the c=c that already has the greatest number of hydrogen atoms bonded to it
What is the mechanism of halogen at ion
In book read now
What is the mechanism of hydrohalogenation
In book read now
What is the mechanism of acid-catalysed hydration
In book read now
Amines form hydrogen bonds between molecules, in tertiary amines. They are no hydrogens attached directly to the nitrogen so hydrogen bonding between the molecules is impossible
Primary amines can form hydrogen bonds most easily so will have the highest MP/BP, tertiary will have the lowest
.
what is homiletic fission
homilytic fission results in the formation of two neutral radicals this occurs when each atom retains one electron from the covalent bond and breaks evenly this normally occurs when non polar covalent bonds are broken
what is heterolytic fission
heterolytic fission results in the formation of two oppositely charged ions. this occurs when one atom retains both electrons from the sigma covalent bonds and the bond breaks unevenly. it normally occurs when polar covalent bonds are broken
