How do I produce an R value for the following data?

time_2 = [0.2572 1.3918 2.9652 4.2965 6.1876 7.8971];
conc_2 = [0.2134 0.1638 0.1241 0.0720 0.0149 -0.0447];

figure
plot(time_2,conc_2)
title('Data Set 2')
xlabel('Time')
ylabel('Concentration')

coeffs = polyfit(time_2,conc_2,1);
fittedX = linspace(min(time_2), max(time_2), 200);
fittedY = polyval(coeffs, fittedX);
hold on;
plot(fittedX, fittedY, 'r-');

Answer 1

[Von Duesenberg]

In your case, with a polynomial of degree 1, you are pretty much assessing to whant extent the relationship between your two variables follow a straight line; maybe a simple correlation coefficient is what you want:

corrcoef(time_2, conc_2)