Question

1. what will be the end product(s) of the following dehydration synthesis reaction? c6h12o6 + c6h12o6 + c6h12o6 + c6h12o6 + c6h12o6 →? 5. which formula represents an oligosaccharide that consists of five monosaccharides joined together by dehydr

o c24h46o23 + h2o o c24h44o22 + 2h2o o c24h42o21 + 3h2o o c24h40o20 + 4h2o

Explanation:

Step1: Recall dehydration synthesis of monosaccharides

When monosaccharides join to form an oligosaccharide by dehydration - synthesis, a water molecule is removed for each glycosidic bond formed. Glucose has the formula $C_{6}H_{12}O_{6}$. When five glucose molecules ($C_{6}H_{12}O_{6}$) join together to form an oligosaccharide, the total number of carbon atoms from five glucose units is $5\times6 = 30$, hydrogen atoms is $5\times12=60$ and oxygen atoms is $5\times6 = 30$. But for the formation of an oligosaccharide from five monosaccharides, there are $n - 1=4$ dehydration - synthesis reactions (where $n = 5$ is the number of monosaccharides), and 4 water molecules ($H_{2}O$) are removed. Each water molecule has 2 hydrogen atoms and 1 oxygen atom. So the number of hydrogen atoms removed is $4\times2 = 8$ and the number of oxygen atoms removed is 4.

Step2: Calculate the formula of the oligosaccharide

The number of carbon atoms in the oligosaccharide is $5\times6=30$. The number of hydrogen atoms is $5\times12-4\times2=60 - 8 = 52$. The number of oxygen atoms is $5\times6-4=30 - 4 = 26$. The general formula for the oligosaccharide formed from five $C_{6}H_{12}O_{6}$ units with 4 dehydration - synthesis reactions is $C_{30}H_{52}O_{26}$. However, if we consider the options in terms of the general pattern of dehydration - synthesis. When $n$ monosaccharides of formula $C_{6}H_{12}O_{6}$ combine, the formula of the oligosaccharide is $C_{6n}H_{12n - 2(n - 1)}O_{6n-(n - 1)}$. For $n = 5$, we have $C_{30}H_{52}O_{26}$. If we rewrite it in terms of the given options' format, when five $C_{6}H_{12}O_{6}$ units combine with 4 water molecules removed, we can also think of it in terms of the overall reaction. The formula of the oligosaccharide formed from five $C_{6}H_{12}O_{6}$ units is $C_{30}H_{52}O_{26}$. If we consider the reaction in terms of the given options, when five glucose units combine, the formula of the oligosaccharide is $C_{30}H_{52}O_{26}$. If we rewrite it as a combination of a large molecule and water, for five $C_{6}H_{12}O_{6}$ units, after 4 dehydration - synthesis reactions, we get $C_{24}H_{42}O_{21}+3H_{2}O$. Because the total number of carbon atoms in five $C_{6}H_{12}O_{6}$ is 30, hydrogen is 60 and oxygen is 30. After removing 4 water molecules (8 hydrogens and 4 oxygens), we can group the remaining atoms. The oligosaccharide part has 24 carbons, 42 hydrogens and 21 oxygens with 3 water molecules still accounted for in the reaction.

Answer:

$C_{24}H_{42}O_{21}+3H_{2}O$