Question

What is meant by inversion of sugar?

Answer 1

Carbohydrates are the organic molecules having carbon, hydrogen and oxygen. These organic molecules make up monosaccharide, disaccharides and polysaccharides that are the sweet carbohydrates also called sugars. Sugars having aldose or ketose consist of optical activity, which is laevorotatory and dextrorotatory.

Complete answer:
Sugars are carbohydrates that are organic molecules having carbon, hydrogen and oxygen. Sucrose is a type of non - reducing disaccharide sugar that is made of aldohexose (6 – C with aldehyde group) glucose and a ketohexose (6 – C with a ketone group) fructose.
When an optically active molecule is able to rotate the plane polarized in clockwise direction it is called dextrorotatory (+). When the molecule rotates the PPL in anti clockwise direction then it is called laevorotatory (-). Sucrose is sugar that is dextrorotatory.
On hydrolysis of sucrose we can obtain glucose and fructose that have different types of rotation for PPL. Fructose has a levorotation of $-92.4{}^\circ$, while glucose has a dextrorotation of$+52.5{}^\circ$. Since the laevorotation is more than dextrorotation, so the overall rotation becomes laevorotation as:
$\begin{aligned} & {{C}_{12}}{{H}_{22}}{{O}_{11}}+{{H}_{2}}O\to {{C}_{6}}{{H}_{12}}{{O}_{6}}+{{C}_{6}}{{H}_{12}}{{O}_{6}} \\\ & sucrose\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\alpha \,glu\cos e\,\,\,\,\,\,\,\beta \,fructose \\\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,+{{52.5}^{o}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,-{{92.4}^{o}} \\\ \end{aligned}$
So, sucrose on hydrolysis brings about a change in rotation from dextrorotatory to laevorotatory. This is called the inversion of sugar.

Note:
Sucrose is a disaccharide formed by the carbon – 1 and carbon – 4 linkages of glucose and fructose respectively. It is non – reducing as the aldehyde and the ketone in glucose and fructose are not free and linked through glycosidic linkage. So, sucrose on hydrolysis forms glucose and fructose as$\begin{aligned} & {{C}_{12}}{{H}_{22}}{{O}_{11}}+{{H}_{2}}O\to {{C}_{6}}{{H}_{12}}{{O}_{6}}+{{C}_{6}}{{H}_{12}}{{O}_{6}} \\\ & sucrose\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\alpha \,glu\cos e\,\,\,\,\,\,\,\beta \,fructose \\\ \end{aligned}$ .