alkenes Flashcards
(15 cards)
what does unsaturated mean
A molecule containing one or more multiple carbon to carbon bonds
How do C=C bonds act when you try to rotate them? Why?
The double bond restricts rotation because the pi bond locks the carbon atoms into place.
Describe and explain the shape around one of the C atoms in an ethene molecule. Give the name and bond angle for the shape
The shape around each carbon atom in the double bond is trigonal planar. This is because there are three regions of electron density. These regions of electron density repel each other and get as far apart as possible. The bond angle is 120˚.
Give the definition of the term stereoisomers
Stereoisomers are molecules that have the same structural formula but a different arrangement of atoms in space.
Explain the term E/Z isomerism and give the conditions necessary for a molecule to exhibit E/Z isomerism
E/Z isomerism is caused by the restricted rotation about the double bond. This means that the atoms bonded to each carbon atom in the double bond are fixed in their positions relative to one another. In order to exhibit E/Z isomerism, the molecule must have a C=C bond and each C in the double bond must have two different atoms or groups attached. The E isomer has the same / priority groups diagonally opposite and the Z isomer has the same / priority groups on the same side
Explain the term cis–trans isomerism
In cis-trans isomers, one of the atoms attached to each carbon atom, must be hydrogen. The trans isomer has the hydrogen atoms diagonally opposite each other (E), and the cis isomer has the hydrogen atoms on the same side (Z).
Give some examples of how you would use Cahn–Ingold–Prelog (CIP) priority rules to identify the E and Z stereoisomers?
The atoms attached to each C atom in the double bond are assigned a priority based on their atomic number. The higher the atomic number, the higher the priority. If the priority groups are on the same side of the double bond, then the compound is the Z isomer. If they are diagonally opposite, the compound is the E isomer.
Give the main reasons that alkenes are reactive
The pi bond in the alkene is weaker than a sigma bond and so this breaks relatively easily. Alkenes are unsaturated and so molecules can add across the double bond. The double bond is an area of high electron density which is localised between the carbon atoms – this makes alkenes attractive to electrophiles.
What is the test for an alkene? Give the reagents and what you would observe.
The test for an alkene is to add bromine water. The bromine water is an orange solution and this decolourises when it reacts with an alkene.
define the term electrophile
electron pair donor
Can you use Markownikoff’s rule to predict formation of a major organic product in addition reactions of H–X to unsymmetrical alkenes (e.g. H–Br to propene) in terms of the relative stabilities of carbocation intermediates in the mechanism?
The major organic product is formed from the more stable carbocation intermediate. Tertiary carbocations are more stable than secondary carbocations which are in turn more stable than primary carbocations.
List and describe the benefits for sustainability of processing waste polymers by combustion for energy production?
Some waste polymers are difficult to recycle but they can be incinerated to produce electricity for heating homes. By doing this, they are not going to landfill.
List and describe the benefits for sustainability of processing waste polymers by use as an organic feedstock for the production of plastics and other organic chemicals
Polymers can be processed and turned into the monomer molecules again. These can then be used to make new chemicals. The waste does not go to landfil and the resource is used for another purpose rather than being wasted
List and describe the benefits for sustainability of processing waste polymers by removal of toxic waste products formed during disposal by combustion of halogenated plastics (e.g. PVC)?
When burned, PVC releases hydrogen chloride, an acidic gas and dioxins, toxic gases. Dumping PVC in landfill sites is not sustainable. The PVC can be ground up or dissolved in a solvent and used to make new PVC products.
List and describe benefits to the environment of development of biodegradable and photodegradable polymers?
These polymers are renewable and sustainable. Biodegradable polymers can be broken down by microorganisms. Photodegradable polymers contain bonds that are weakened by light which starts the degradation process
