Skip to main content

What is the chemical test for alkanes and alkenes?

Alkanes and alkenes are both hydrocarbons. Alkanes, however, contain only single bonds between the carbons while alkenes contain at least one double bond between carbons. Tests can be conducted to differentiate these two groups of molecules based on whether or not the double bonds can be broken by a halogen.


If one takes two test tubes with bromine water and adds an alkene to tube A and an alkane to tube B and then shakes...

Alkanes and alkenes are both hydrocarbons. Alkanes, however, contain only single bonds between the carbons while alkenes contain at least one double bond between carbons. Tests can be conducted to differentiate these two groups of molecules based on whether or not the double bonds can be broken by a halogen.


If one takes two test tubes with bromine water and adds an alkene to tube A and an alkane to tube B and then shakes the two tubes, a color change will occur in tube A (the color of the solution will change from brown to colorless) while no color change will occur in tube B. This is because in tube A, the double bond is broken and the carbons become halogenated while no reaction occurs in tube B.


The reaction that occurs in tube A is as follows:


Bromine is a diatomic element. It regularly occurs as Br2. In a molecule of Br2 one bromine has a partial positive charge and the other has a partial negative charge. It only becomes polarized as it approaches the electron-dense double bond of the alkene.


The electrophilic bromine attacks the double bond and a bond is formed between one of the carbons involved in the double bond and the electrophilic bromine. The other bromine is a good leaving group and leaves as a bromine ion.  


This leaves the former alkene as a carbo-cation; there is a positive charge on the carbon that now only has three bonds (due to the breaking of the double bond). This is an unstable intermediate, but the positive carbon is then attacked by the negative bromine ion and a bond is formed. The resulting product is 1,2-dibromoethane which is colorless while diatomic bromine is dark red/brown.  

Comments

Post a Comment

Popular posts from this blog

How and why does James Gatz become Jay Gatsby? Describe the young Gatsby/Gatz.

James Gatz, a poor Midwestern boy of probable Jewish lineage, becomes Jay Gatsby, a presumed WASP and wealthy socialite, when he moves to New York City and acquires his fortune. It is wealth that has allowed Gatz to transform himself into Gatsby. However, those who know his background (e.g., Daisy and Tom Buchanan) never allow him to forget that he is nouveau riche -- that is, an upstart who has just recently made his fortune,... James Gatz, a poor Midwestern boy of probable Jewish lineage, becomes Jay Gatsby, a presumed WASP and wealthy socialite, when he moves to New York City and acquires his fortune. It is wealth that has allowed Gatz to transform himself into Gatsby. However, those who know his background (e.g., Daisy and Tom Buchanan) never allow him to forget that he is nouveau riche -- that is, an upstart who has just recently made his fortune, whereas they arose from well-to-do families. Gatz became Gatsby through determination and discipline. At the end of the novel, the narr...
Post a Comment
Read more

What gift did Della buy for Jim and why in "The Gift of the Magi" by O. Henry?

Della buys Jim a watch fob because his watch is his most prized possession. Della and Jim Young do not have much money. Despite this, Della really wants to buy Jim a good Christmas present. She is even willing to sell her hair to get him a nice gift. This is ironic because we learn Della and Jim both highly prize her hair. Now, there were two possessions of the James Dillingham Youngs in which... Della buys Jim a watch fob because his watch is his most prized possession. Della and Jim Young do not have much money. Despite this, Della really wants to buy Jim a good Christmas present. She is even willing to sell her hair to get him a nice gift. This is ironic because we learn Della and Jim both highly prize her hair. Now, there were two possessions of the James Dillingham Youngs in which they both took a mighty pride. One was Jim's gold watch that had been his father's and his grandfather's. The other was Della's hair.  Della is still willing to sell her hair so she can b...
Post a Comment
Read more

Explain and discuss how the definitions of freedom change for the nation, for the freedmen and for southern whites after the Civil War.

After the Civil War, the definition of freedom changed in the nation, as slavery was ended with the 13th Amendment to the Constitution in 1865. The practice of slavery was disallowed, but definition of the freedom that would take its place was a subject of controversy, ongoing debate, and even violence in the decades to come.  For freedmen, freedom often meant reconciling with their families, who were broken up by slavery; choosing which church to... After the Civil War, the definition of freedom changed in the nation, as slavery was ended with the 13th Amendment to the Constitution in 1865. The practice of slavery was disallowed, but definition of the freedom that would take its place was a subject of controversy, ongoing debate, and even violence in the decades to come.  For freedmen, freedom often meant reconciling with their families, who were broken up by slavery; choosing which church to belong to without being ordered to attend religious services (or not to attend) by their mast...
Post a Comment
Read more